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                                                                  EXHIBIT 10.50






                           MASTER LEASE AGREEMENT

                               BY AND BETWEEN

                    LCOR CLARKSBURG L.L.C., AS LANDLORD

                                    AND

                       COMSAT CORPORATION, AS TENANT





                  CLARKSBURG, MONTGOMERY COUNTY, MARYLAND







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                             TABLE OF CONTENTS




INTRODUCTION
Section 1.  DEFINITIONS......................................................1
Section 2.  LEASE OF MASTER LEASE PROPERTY...................................2
Section 3.  TERM.............................................................2
Section 4.  RENT.............................................................4
Section 5.  USE OF THE MASTER LEASE PROPERTY.................................7
Section 6.  DEVELOPMENT; DESIGNATION OF THE EXCLUDED AREAS...................9
Section 7.  TAXES AND IMPOSITIONS...........................................11
Section 8.  UTILITIES.......................................................15
Section 9.  SIGNS...........................................................15
Section 10. AS-IS CONDITION OF MASTER LEASE PROPERTY........................16
Section 11. REPAIRS, MAINTENANCE AND MANAGEMENT.............................16
Section 12. ACCESS TO MASTER LEASE PROPERTY.................................18
Section 13. ALTERATIONS AND PERSONAL PROPERTY...............................19
Section 14. INSURANCE.......................................................22
Section 15. DAMAGE OR DESTRUCTION...........................................25
Section 16. INDEMNIFICATION.................................................31
Section 17. CONDEMNATION....................................................35
Section 18. LIENS...........................................................36
Section 19. EXISTING SPACE LEASES; ASSIGNMENT AND SUBLETTING................37
Section 20. SUBORDINATION OR SUPERIORITY OF LEASE...........................40
Section 21. DEFAULTS AND REMEDIES...........................................40
Section 22. BANKRUPTCY OR INSOLVENCY........................................45
Section 23. SURRENDER OF MASTER LEASE PROPERTY..............................47
Section 24. NON-CONSENSUAL HOLDING OVER.....................................48
Section 25. QUIET ENJOYMENT.................................................48
Section 26. NOTICES.........................................................48
Section 27. HAZARDOUS MATERIALS.............................................49
Section 28. RIGHT TO RENEW TERM.............................................52
Section 29. SECURITY DEPOSIT................................................54
Section 30. MISCELLANEOUS GENERAL PROVISIONS................................54

SCHEDULE I  Defined Terms
SCHEDULE II Deductibles
SCHEDULE OF EXHIBITS

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                           MASTER LEASE AGREEMENT


                  THIS LEASE  AGREEMENT  (this "Lease") is entered into and
made  effective  as of the  12th day of  September,  1997  (the  "Effective
Date"), by and between LCOR CLARKSBURG L.L.C., a Delaware limited liability
company  ("Landlord")  and  COMSAT  Corporation,  a  District  of  Columbia
corporation ("Tenant").

                                WITNESSETH:

                  (a) Prior to but contemporaneously with the execution and
delivery  of this  Lease,  Tenant  sold and  transferred  the Master  Lease
Property to Landlord  pursuant to that certain  Agreement of Sale dated the
Effective  Date,  by and  between  Tenant,  as  seller,  and  Landlord,  as
purchaser (the "Purchase and Sale Agreement").

                  (b)  Landlord  desires  to lease to  Tenant,  and  Tenant
desires to lease back from Landlord,  the Master Lease Property, all as set
forth and on the terms and conditions contained in this Lease.

                  NOW THEREFORE,  in  consideration  of the mutual promises
set forth in this  Lease and other  good and  valuable  consideration,  the
receipt and sufficiency of which are  acknowledged by each party,  Landlord
and Tenant agree as follows:

                  SECTION 1.        DEFINITIONS

                  (a) The following terms shall have the meanings  ascribed
thereto below:

                  Agents:  The agents, employees, contractors,
subcontractors, affiliates, licensees and invitees of each party
(and in the case of Tenant, subtenants).

                  Excluded Areas:  Any areas of the Master Lease Property
excluded by Landlord pursuant to Section 6.

                  Expiration Date:  The ending date of the Term.

                  Installations  Premises:  Certain portions of the Land as
described  or shown on  Exhibit C attached  hereto and made a part  hereof,
together with all improvements located thereon.

                  Land:   Approximately   227  acres  of  land  located  in
Clarksburg, Montgomery County, Maryland, as described or shown on Exhibit A
attached hereto and made a part hereof.

                  Main  Building:  A building  complex  consisting of three
buildings  (the  "Component  Buildings")  which,  for the  purposes of this
Lease,  Landlord and Tenant agree contain, in the aggregate,  496,000 gross
square feet of space (the "Main Building  Space"),  located on the Land and
commonly known as 22250, 22300, and 22240

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COMSAT  Drive,  Clarksburg,  Maryland.  Further,  for the  purposes of this
Lease,   Landlord  and  Tenant  agree  that  the  Component  Buildings  are
designated as, and contain amounts of Main Building Space, as follows:

                  Building A:  The largest of the Component Buildings,
                  commonly known as the primary building; 446,000 gross
                  square feet;

                  Building B:  The second largest of the Component
                  Buildings, commonly known as the Spectra building;
                  40,000 gross square feet;

                  Building  C: The  smallest  of the  Component  Buildings,
                  commonly  known  as the  etching  and  plating  building;
                  10,000 gross square feet.

                  Main  Building  Area:  The Main  Building and the Parking
Areas,  access  drives,  and  other  appurtenant  areas  serving  the  Main
Building,  as  described  or shown on Exhibit B attached  hereto and made a
part hereof.

                  Master Lease Property:  The Land, together with all
improvements located thereon, less the Installations Premises and
the Excluded Areas.  The Master Lease Property includes, without
limitation, the Main Building Area.

                  Parking Areas:  Those certain areas located in the Main
Building Area and designated for use for parking of motor
vehicles as of the Effective Date.

                  Unimproved Area:  The Master Lease Property, less the
Main Building Area.

                  (b) Other  terms  shall have  meanings  ascribed  to such
terms in this Lease and as shown on  Schedule I attached  hereto and made a
part hereof.

                  SECTION 2.        LEASE OF MASTER LEASE PROPERTY

                  Landlord,   for  and  in   consideration  of  the  rents,
covenants and agreements  hereinafter reserved,  mentioned and contained on
the part of Tenant and its  successors  and assigns,  to be paid,  kept and
performed,  has leased, rented, let and demised, and by these presents does
lease,  rent,  let and demise unto Tenant,  and Tenant does hereby take and
hire,   upon  and  subject  to  the  covenants,   agreements,   provisions,
limitations and conditions herein expressed, the Master Lease Property.

                  SECTION 3.        TERM

                  (a) The initial term of this Lease (the  "Initial  Term")
shall be for a period of ten (10) years  commencing on the  Effective  Date
and  ending  at  11:59  p.m.  local  time on the day  preceding  the  tenth
anniversary of the Effective Date, unless

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this  Lease  shall be  sooner  terminated  as  hereinafter  provided  or as
provided by law. Notwithstanding the foregoing, if the Term ends on any day
other than the last day of any calendar  month,  the Term shall be extended
so that the last  day of the Term is the last day of such  calendar  month.
The Initial  Term,  as may be extended  by  exercise of the  provisions  of
Subsection 3(b) or Section 28, may sometimes be collectively referred to in
this Lease as the "Term".

                  (b) Provided that no Event of Default  exists on the date
of the Holdover Notice or the date of commencement of the Holdover  Period,
Tenant may holdover  under the terms of this Lease with respect to the Main
Building Area for up to six (6) months  immediately after the Initial Term,
provided that:

                           (i)  Tenant provides Landlord with written notice
(the  "Holdover  Notice") at least six (6) months  prior to the  Expiration
Date of the  Initial  Term  stating the number of months up to six (6) that
Tenant will holdover under the terms of this Lease (the "Holdover Period");
and

                           (ii) Tenant pays as Base Rent for each month
during the Holdover Period,  in addition to all other amounts payable under
this Lease, one hundred twelve and 75/100ths  percent (112.75%) of the full
monthly installment of Base Rent due in the last year of the Initial Term.

If Tenant  exercises this holdover right,  then,  upon  commencement of the
Holdover Period,  any portions of the Unimproved Area remaining  subject to
this Lease at the  expiration  of the Initial Term shall  automatically  be
released from this Lease as Excluded  Area as if released  under Section 6;
provided,  however,  that after the  commencement  of the Holdover  Period,
Tenant shall not record any  instrument  confirming  the grant of easements
described in Section  6(d). At its sole  election,  Tenant may exercise its
right to the  Holdover  Period  with  respect  to less than all of the Main
Building  Area. If Tenant  desires to so holdover with respect to less than
all of the Main  Building  Area,  Tenant  shall  designate  in the Holdover
Notice the space in which it desires to holdover in the Main Building,  but
in no event less than two hundred  fifty  thousand  (250,000)  gross square
feet  (including the aggregate gross square footage of the area of the Main
Building then leased under Existing  Space Leases and Subleases,  the terms
of which have been extended  beyond the Expiration Date of the Initial Term
with Landlord's approval) (the "Holdover Space"). Tenant's payments of Base
Rent and payments of  Additional  Rent during the Holdover  Period shall be
reduced  to the  proportion  that  the  Holdover  Space  bears  to the Main
Building  Space and Tenant  shall have the  nonexclusive  right  during the
Holdover  Period to use the Parking  Areas,  access  drives,  and all other
common areas within the Main Building Area. If Tenant  designates a part of
the Holdover  Space in Building B in the Holdover  Notice,  Tenant shall be
required to holdover in the entirety of Building B. If Tenant  designates a
part of the Holdover Space in Building C in the Holdover  Notice,  Tenant

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shall be required to holdover in the  entirety of Building C. The amount of 
square  footage  comprising  the Holdover  Space  designated in Building A 
shall be determined in accordance with the  applicable  standard of the 
Greater Washington Association of Commercial Realtors and such  Holdover
Space shall be so configured as to leave remaining space in Building A 
reasonably  marketable to third party tenants;  provided,  however,  this 
obligation  shall not require Tenant to construct Alterations in order to leave
such a marketable space.

                  (c). As used in this  Lease,  the term  "Lease  Year" means
each  consecutive  period of twelve (12)  calendar  months during the Term,
commencing on the Effective Date. If, however,  the Effective Date is other
than the first day of a calendar month, the first Lease Year shall begin on
the Effective Date and end on the first  anniversary of the last day of the
calendar month in which the Effective Date falls, and each succeeding Lease
Year shall be each  succeeding  consecutive  period of twelve (12) calendar
months thereafter during the Term.

                  SECTION 4.        RENT

                  (a) Tenant covenants and agrees to pay Landlord in lawful
money of the United States,  annual base rent for the Master Lease Property
("Base Rent") in twelve (12) equal monthly installments,  in advance, on or
before  the first  day of each and  every  month  throughout  the Term,  as
follows:

                  (i) FOUR MILLION NINE HUNDRED  SIXTY  THOUSAND AND NO/100
DOLLARS ($4,960,000.00) during the first Lease Year.

                  (ii) FIVE  MILLION  NINETY-SIX  THOUSAND AND FOUR HUNDRED
AND NO/100 DOLLARS ($5,096,400.00), during the second Lease Year.

                  (iii) FIVE MILLION TWO HUNDRED  THIRTY-SIX  THOUSAND FIVE
HUNDRED  FIFTY-ONE  AND NO/100  DOLLARS  ($5,236,551.00),  during the third
Lease Year.

                  (iv) FIVE MILLION  THREE  HUNDRED  EIGHTY  THOUSAND  FIVE
HUNDRED  FIFTY-SIX AND 15/100  DOLLARS  ($5,380,556.15),  during the fourth
Lease Year.

                  (v) FIVE MILLION FIVE HUNDRED TWENTY-EIGHT  THOUSAND FIVE
HUNDRED  TWENTY-ONE  AND 45/100 DOLLARS  ($5,528,521.45),  during the fifth
Lease Year.

                  (vi)  FIVE  MILLION  SIX  HUNDRED  EIGHTY  THOUSAND  FIVE
HUNDRED  FIFTY-FIVE  AND 79/100 DOLLARS  ($5,680,555.79),  during the sixth
Lease Year.

                  (vii) FIVE  MILLION  EIGHT  HUNDRED  THIRTY-SIX  THOUSAND
SEVEN HUNDRED  SEVENTY-ONE AND 07/100 DOLLARS  ($5,836,771.07),  during the
seventh Lease Year.


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                  (viii) FIVE MILLION NINE  HUNDRED  NINETY-SEVEN  THOUSAND
TWO HUNDRED EIGHTY-TWO AND 27/00 DOLLARS ($5,997,282.27), during the eighth
Lease Year.

                  (ix) SIX  MILLION  ONE  HUNDRED  SIXTY-TWO  THOUSAND  TWO
HUNDRED SEVEN AND 54/100  DOLLARS  ($6,162,207.54),  during the ninth Lease
Year.

                  (x) SIX MILLION  THREE  HUNDRED  THIRTY-ONE  THOUSAND SIX
HUNDRED  SIXTY-EIGHT AND 24/100 DOLLARS  ($6,331,668.24),  during the tenth
Lease Year.

Notwithstanding  the foregoing,  if the Effective Date shall be a day other
than the first day of a calendar  month,  there shall be due and payable on
the Effective  Date, as the  installment  of Base Rent for such  fractional
month,  an amount  determined by dividing the Base Rent for the first Lease
Year by 365 and  multiplying  the  result  by the  number  of days from the
Effective Date through the end of such month.

                  (b)  Tenant  also   covenants   and  agrees  to  pay,  as
additional rent (the  "Additional  Rent"),  all sums,  Impositions,  costs,
expenses and other  payments  which Tenant in any of the provisions of this
Lease  assumes,  agrees  or is  obligated  to pay,  or which  shall  become
otherwise  due and payable from Tenant to Landlord  under this Lease (other
than  Base  Rent).   Base  Rent  and  Additional   Rent  may  sometimes  be
collectively referred to herein as "Rent".

                  (c) It is the purpose  and intent of Landlord  and Tenant
that,  except as  explicitly  set  forth  herein,  the Base  Rent  shall be
absolutely  net to  Landlord,  so  that  this  Lease  shall  yield,  net to
Landlord, the net annual rent specified in Subsection (a) of this Section 4
in each  Lease  Year  during  the Term and that  all  costs,  expenses  and
obligations  of every kind and nature  whatsoever,  in  connection  with or
relating to the Master Lease Property shall be the obligation of Tenant and
shall be paid by Tenant.

                  (d) The Base Rent shall be paid to Landlord promptly when
due without notice or demand therefor, and without any abatement (except as
explicitly stated to the contrary in Section 8, Section 15 and Section 17),
deduction or set-off for any reason whatsoever.

                  (e) No  payment by Tenant or  receipt  or  acceptance  by
Landlord of a lesser  amount  than the  correct  Rent shall be deemed to be
other than a payment on account,  nor shall any endorsement or statement on
any check or any  letter  accompanying  any check or  payment  be deemed an
accord and  satisfaction,  and  Landlord  may accept  such check or payment
without  prejudice to Landlord's right to recover the balance or pursue any
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                  (f) If any  of the  Rent  payable  under  the  terms  and
provisions  of this  Lease  shall be or become  uncollectible,  reduced  or
required to be refunded  because of any rent  control or similar act or law
enacted by a valid  governmental  authority,  Tenant  shall enter into such
agreements and take such other steps that  Landlord  may  request  and as may
be legally  permissible  to permit Landlord to collect the maximum  rents 
which,  from time to time during the continuance of such legal rent 
restriction, may be legally permissible (and not in excess of the amounts 
reserved therefor under this Lease).  Upon the termination of such legal rent
restriction,  (i) the Rent shall become and thereafter be payable in accordance
with the amounts  reserved  herein for the periods following such termination,
and (ii) Tenant shall promptly pay to Landlord, to the maximum extent legally
permissible,  an amount equal to (a) the Rent which would have been paid 
pursuant to this Lease but for such legal rent restriction,  less (b) the Rent
paid by Tenant during the period such rent restriction was in effect.

                  (g) All Rent and other  payments  required  to be made by
Tenant to Landlord shall be delivered to Landlord by wire transfer pursuant
to the wire transfer instructions as shown on Exhibit D attached hereto and
made a part hereof or to any other single  party that  Landlord may specify
from time to time by written notice given to Tenant.

                  (h)  In  recognition  of  the  extra  costs  to  Landlord
resulting from Tenant's  failure to make timely payment of any  installment
of Base Rent,  if any such  installment  is not paid  within  nine (9) days
after its due date,  the  delinquent  amount  shall be subject to a service
charge of five  percent  (5%) of such  delinquent  amount,  or such  lesser
charge as may be the maximum charge  permitted by law. In addition,  if any
installment  of Base Rent or any other sum due  Landlord  under  this Lease
remains unpaid  seventy-five  (75) days after its due date, the outstanding
amount  shall bear  interest at an annual rate of two percent (2%) over the
"Prime Rate" then prevailing or such lesser rate as may be the maximum rate
permitted by law (the "Stipulated  Rate"), and calculated from the due date
of such sum and  continuing  through the date such sum is paid in full.  As
used in this Lease,  the term "Prime Rate" means the prime rate of interest
for large money center banks as published in the Money Rates section of the
Wall Street  Journal or if the Wall Street  Journal  ceases to publish such
rate, as established  by reference to such other  authority as is generally
accepted in the business  community as a source for  determining the "Prime
Rate".

                  SECTION 5.        USE OF THE MASTER LEASE PROPERTY

                  (a) The Main  Building  may be occupied  and used for any
lawful purpose and shall not be used for any other  purpose.  The remainder
of the Main Building Area may be occupied and used for parking for, access to, 

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and other reasonable  purposes incidental to use of the  Main  Building  and
shall  not be used  for any  other  purpose.  The Unimproved  Area shall not
be  occupied by Tenant but may be used by Tenant for (i)  access  to the  Main
Building  Area  via  roads  existing  in the Unimproved  Area  as of the 
Effective  Date,  or as may  be  relocated  as expressly provided for in this
Lease, (ii) purposes which are incidental to use of the  Main  Building  Area,
such as use,  maintenance,  repair,  and replacement of utilities, storm 
drainage facilities, and signage serving or used in connection  with the Main
Building Area, (iii) use,  maintenance, repair, and replacement of antennae, 
satellite dishes, and other communications equipment located in the Unimproved
Area as of the Effective Date (but such facilities, excluding footings, 
foundations, and concrete bases, shall be removed by Tenant at its own expense
promptly after such Unimproved Area is excluded from this Lease under 
Section 6),  (iv)reasonable  recreation  uses,  such  as use of  the  existing
recreational facilities,  (v) temporary activities and uses that Tenant
reasonably deems desirable,  and (vi) such limited  purposes as are reasonably
necessary in order for Tenant to fulfill  its  obligations  under this Lease to
Care for the Unimproved Area.  Notwithstanding anything to the contrary
contained in this Lease,  with  respect to the uses  described  in clauses
(iv) and (v) above, (y) the Tenant shall ensure that such uses do not interfere
with the Development,  and (z) no action or  omission  of  Landlord,  or its
Agents, successors and assigns that interferes with such uses shall be a
default of Landlord under this Lease.

                  (b)      Tenant further agrees as follows:

                           (i)    Tenant and its Agents shall use the Master
Lease  Property  and  conduct  its  business  thereon  in a safe,  careful,
reputable and lawful manner.

                           (ii)   Tenant shall obtain, or cause to be obtained,
all   certificates,   licenses  and  permits  necessary  for  its,  or  its
subtenants',  occupancy, use, operation and maintenance of the Master Lease
Property.  Upon  reasonable  advance  request  by  Tenant,  Landlord  shall
reasonably  cooperate  with Tenant in  Tenant's  obtaining  such  necessary
certificates,  licenses or permits, including, without limitation,  signing
applications  for the same  within ten (10)  business  days after  Tenant's
request if Landlord's signing is required by Applicable Law or requested by
a governmental authority;  provided, that Landlord shall not be required to
incur any  out-of-pocket  costs to third parties in  connection  therewith.
Tenant  shall  promptly  reimburse  Landlord  for  any  of  its  reasonable
out-of-pocket costs to third parties for review or advice about such 
certificates, licenses or permits.

                           (iii)  Tenant shall not commit, nor allow to be
committed,  in, on or about the Master  Lease  Property,  any act of waste,
including  any act which might  deface,  damage or destroy any  improvement
thereon, or any part thereof. Further, Tenant shall not permit any noise or
odor to be emitted  from the Master  Lease  Property  which is  unlawful or
which constitutes a legal nuisance.  Notwithstanding the foregoing,  Tenant

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shall not have any responsibility for any waste, noise, or odor caused by
Landlord or its Agents.

                           (iv)   Tenant shall promptly comply in all material
respects  with all present and future laws,  statutes,  ordinances,  rules,
regulations and orders of any federal, state, municipal or other government
or  agency  thereof  having  jurisdiction  over  and  relating  to the use,
condition and occupancy of the Master Lease  Property,  and any  covenants,
conditions and restrictions of record existing as of the Effective Date and
governing the Master Lease Property (collectively,  the "Applicable Laws").
Tenant  acknowledges that the Applicable Laws are of public record and that
Tenant knows the character of its  operation on the Master Lease  Property.
Tenant  shall  have  sole   responsibility  for  its  compliance  with  the
Applicable  Laws in all material  respects,  and  Tenant's  inability to so
comply   shall  not  be  cause  for  Tenant  to   terminate   this   Lease.
Notwithstanding the foregoing:

                                    (A) Tenant shall not be required to comply
with any  Applicable  Laws to the extent  that  Tenant or the Master  Lease
Property are legally  grandfathered  or exempt from the application of such
Applicable  Laws or Tenant may obtain from the  appropriate  authorities  a
waiver or variance with respect to compliance.

                                    (B) Tenant shall not be required to comply
with any legal  requirements  in connection  with the Master Lease Property
arising out of or relating to the  Development or arising out of other acts
or  omissions  of Landlord  or its Agents on or with  respect to the Master
Lease Property. All of such requirements on the Master Lease Property shall
be promptly complied with by Landlord in all material respects,  at its own
expense.

                                    (C) Tenant shall not be obligated to 
correct any violations of Applicable Laws which may exist on the Master Lease
Property  as of the  Effective  Date,  except  to the  extent  specifically
required to do so by written notice from the governmental  authority having
jurisdiction.

                                    (D) Tenant shall have the right to contest
by appropriate legal proceedings,  conducted  diligently and in good faith,
without expense to Landlord,  the validity or application of any Applicable
Laws. If compliance  with the Applicable Law being contested may legally be
delayed  pending  the  prosecution  of the  proceeding,  Tenant  may  delay
compliance until the final determination of the proceeding.  Landlord shall
execute and deliver, within ten (10) business days after request by Tenant,
any appropriate  papers and/or other  instruments  that may be necessary to
permit Tenant to contest the validity or application of the Applicable Law.
Landlord shall otherwise  reasonably  cooperate with Tenant in the contest,
provided  that  Landlord  shall not be required to incur any  out-of-pocket
costs  to  third  parties  in  connection  therewith.  Notwithstanding  the

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foregoing, Tenant shall ensure that any such contest does not cause any lien 
to be filed against the Master Lease Property or any portion thereof.

                  SECTION 6. DEVELOPMENT; DESIGNATION OF THE EXCLUDED
                                     AREAS

                  (a)  Tenant  acknowledges  that,  among  other  purposes,
Landlord  purchased  the Master Lease  Property  for  possible  development
and/or sale of all or portions of the Unimproved Area. Although Landlord is
not  required to develop or sell any of the  Unimproved  Area,  Landlord is
contemplating a mixed-use  development thereon,  consisting of, among other
things, uses of varying densities, sizes and natures, and infrastructure in
order to serve same (all or any portion thereof,  the  "Development").  The
Development shall be at Landlord's sole cost. Tenant  acknowledges that the
Development  may require  Landlord to change the zoning  classification  as
well as take  other  actions to change  the land use and  character  of the
Master Lease Property.  Tenant covenants and agrees that during the Term it
shall not object to, and shall  reasonably  cooperate  with  Landlord  with
respect  to,  Development  by  Landlord  or  its  successors  of any of the
Unimproved Area and shall reasonably  cooperate so as to avoid interference
with the Development. Notwithstanding the foregoing:

                           (i)  The Development by Landlord shall not
interfere with Tenant's or its subtenants' use of the Master
Lease Property.

                           (ii) No rezoning or other development approvals
sought by Landlord for all or any part of the Master Lease  Property  shall
prohibit,  restrict,  or make  non-conforming  any of the uses which may be
conducted on the Main Building Area or Installations Premises under the I-3
zoning applicable to such property as of the Effective Date.

                           (iii)  Landlord acknowledges that the
uninterrupted   operation  of  antennae,   satellite   dishes,   and  other
communications  equipment  now  or in the  future  installed  on  the  Main
Building Area (the  "Communications  Facilities") is of critical importance
to  Tenant.  Landlord  shall  not  oppose  the  installation  or  continued
operation of the Communications
Facilities.

                           (iv)  Tenant shall not be required to incur any
liability  or  out  of  pocket   expense  to  third  parties  in  providing
cooperation to Landlord or its successors with respect to the Development.

                  (b) At any time  during the Term,  without any consent of
Tenant whatsoever,  a portion of the Unimproved Area shall be excluded from
the Master Lease  Property  immediately  upon the  occurrence of any of the
following (each a "Triggering Event"):


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                           (i)  A written notice from Landlord to Tenant
designating  such portion of the  Unimproved  Area as an Excluded Area. The
notice  shall be  accompanied  by a legal  description  and  drawing of the
Excluded Area.

                           (ii)  The transfer of record title to or the
ground lease of such portion of the Unimproved  Area by Landlord to another
party, including entities related to Landlord.

                           (iii)  The commencement of clearing or grading
work for such portion of the  Unimproved  Area (in which event the Excluded
Area shall include the land to be disturbed by the work, any borrow,  fill,
or stockpile  areas,  any areas for staging of equipment or materials,  any
areas upon which sediment control measures are to be implemented).

Landlord may cause  Triggering  Events with respect to as many  portions of
the Unimproved  Area,  and as often,  as Landlord may determine in its sole
and absolute  discretion.  Landlord shall give Tenant written notice of the
occurrence of the  Triggering  Events  described in (ii) and (iii) above at
least thirty (30) days before their  anticipated  dates of occurrence.  The
notice shall be accompanied by a legal description and plat of the Excluded
Area.  It is the  intention of (iii) that no  development  work  whatsoever
shall be performed to any portion of the  Unimproved  Area while it remains
subject to this Lease and that each such  portion  of the  Unimproved  Area
must be excluded from the Master Lease Property before work begins.

                  (c) Upon  exclusion  of an Excluded  Area from the Master
Lease  Property,  Tenant shall have no further rights or obligations  under
this Lease with respect to such Excluded Area.  There shall be no reduction
in Base Rent with  respect to an Excluded  Area,  but  Landlord  and Tenant
shall equitably apportion any Additional Rent with respect to such Excluded
Area as of the date of exclusion and Landlord shall reimburse Tenant at the
time of such  exclusion in an amount equal to (i) any  Impositions  paid by
Tenant,  and (ii) any other  expenses  paid by Tenant  (provided  that such
expenses  are  required to be paid by Tenant under this Lease) with respect
to such Excluded Area and attributable to the period of time beginning with
and  following  the  date  of  exclusion.  Such  reimbursement  shall  be a
condition precedent to exclusions of any property.  In addition,  Landlord,
at its sole  expense  and as a condition  precedent  to  exclusions  of any
property,  shall cause such Excluded Area to be  established  as a separate
tax parcel  for the  purposes  of  Impositions  at the time such  parcel is
excluded.

                  (d) In the event that an Excluded Area contains any road,
utility line,  drainage line,  storm water  management  facility,  sign, or
other  improvement or amenity then being used by Tenant in connection  with
the Main Building Area (collectively, "Appurtenances"), then, automatically
upon  exclusion  of the  Excluded  Area,  Tenant  shall be  deemed  to have
easements for the continued uninterrupted use of the

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Appurtenances  for so long as this Lease  remains in effect.  The easements
provided for in this subsection  shall include the right of Tenant to enter
upon the  Excluded  Area to  inspect,  maintain,  repair,  and  replace the
Appurtenances.  Notwithstanding  the  foregoing,  Landlord may  temporarily
discontinue  any  of the  Appurtenances  for a  period  of  not  more  than
forty-eight   (48)  hours  if  Landlord   provides  Tenant  with  temporary
Appurtenances,  provided such temporary  Appurtenances allow Tenant and its
Agents to use the Master Lease Property  without any material  diminishment
of Tenant's or its Agents' use of the Master Lease Property or any material
interference  with the business  operations of Tenant or its  subtenants on
the Main Building Area.

                  (e) Notwithstanding anything to the contrary contained in
this  Lease,  Tenant  shall  not be  required  to pay for any  incremental,
additional  or increased  Insurance or any  increased  costs of Care of the
Master Lease  Property which are  attributable  to Development or any other
acts or  omissions  of Landlord  or its Agents  with  respect to the Master
Lease Property.

                  (f)  In   addition   to  the   easements   for   existing
Appurtenances  provided for in  Subsection  6(d),  Landlord  shall grant to
Tenant, or to any utility company or governmental  authority  designated by
Tenant,   such  other   easements  for  utilities,   drainage,   stormwater
management,  and other similar matters on, under, and across the Unimproved
Area as may be reasonably  required in connection with the use or occupancy
of the Main Building Area and in  accordance  with this Lease  ("Additional
Easements").  No Additional Easements shall materially and adversely affect
the Development or materially  increase the cost of  Development.  Landlord
shall have a reasonable right of approval of the location of all Additional
Easements.  All Additional Easements shall be granted without charge within
ten (10) business days after written request by Tenant,  accompanied by the
instrument to be executed and a plat showing the location of the Additional
Easement.  Landlord  shall  make  good  faith and  commercially  reasonable
efforts to cause its  mortgagees  to  subordinate  their liens  against the
Master Lease Property to any Additional Easements.

                  SECTION 7.  TAXES AND IMPOSITIONS

                  (a) Tenant  covenants  and agrees to pay,  not later than
the first day on which any  interest or penalty  will accrue or be assessed
for the non-payment  thereof,  all of the following items  applicable to or
affecting the Master Lease Property or any part thereof accruing or payable
from and  after  the  Effective  Date  and  during  the Term or  applicable
thereto:  (i) all real estate  taxes and  assessments  (including,  without
limitation,  assessments  for special  business  improvement  or assessment
districts),  (ii) personal  property taxes,  (iii) occupancy and rent taxes
specifically imposed on tenants in Montgomery County or attributable to the
subtenants of Tenant,  (iv) water and sewer rents,  rates and charges,  (v)
vault taxes and charges,  (vi) certificate,  license and permit fees, (vii)
any taxes, assessments  or  governmental  levies,  general and special,

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ordinary and extraordinary,  foreseen and unforeseen,  of any kind and nature
whatsoever which at any time prior to or during or  applicable to the Term or
any part thereof may be assessed, levied, confirmed, imposed upon, or grow or
accrue or become due and payable out of, or charged  with  respect to, or
become a lien on, the Master Lease Property or any part thereof, or the
sidewalks or streets in front of or adjoining the Master Lease  Property,  or
any vault, passageway or space in, over or under such sidewalk or street, or
any other appurtenances  to the Master  Lease  Property,  or any  personal
property, equipment or other  facility used in the operation  thereof,  or any
use or occupation  of the Master Lease  Property,  or any document by which
Tenant creates or transfers an interest or estate in the Master Lease Property
(except  any  document  releasing  an Excluded  Area from the Master  Lease
Property), and (vii) any fines or penalties or similar governmental charges
applicable with respect to any of the foregoing, together with interest and
costs  thereon (all such items  aforesaid  may  sometimes  be  collectively
referred to herein as "Impositions").

                  (b) If, by law, any  Imposition  imposed during the Term,
which is an assessment not related to general real estate taxes, may at the
option of the  taxpayer be paid in  installments  (whether or not  interest
shall accrue on the unpaid balance of such Imposition), Tenant may exercise
the option to pay the same (and any accrued  interest on the unpaid balance
of such  Imposition)  in  installments  and, in such event,  shall pay such
installments plus interest as may become due during the Term of this Lease;
provided,  that all such payments shall be made before any fine, penalty or
other charge for non-payment of any installment may be added thereto.

                  (c) Any Imposition (including,  without limitation, those
Impositions  which have been converted into installment  payments by Tenant
as referred to in Subsection (b) above)  relating to a period of time which
is partially within the Term and partially beyond the Expiration Date shall
be adjusted  between  Landlord and Tenant as of the Expiration Date so that
Landlord shall pay that portion of such Imposition which is attributable to
any  period of time  after the  Expiration  Date and  Tenant  shall pay the
remainder thereof. This subsection shall survive termination of the Lease.

                  (d)  Notwithstanding  the foregoing,  Tenant shall not be
required to pay municipal, state or federal income, excess profits, capital
levy,  rental  (except  as set forth in clause  (iii) of  Subsection  (a)),
estate,  succession,  inheritance,  transfer,  recordation  (except  to the
extent described in Section 30(v)) or gift taxes of Landlord, any corporate
franchise  tax imposed  upon  Landlord  or any tax  imposed  because of the
nature of the business entity of Landlord;  provided,  however,  that if at
any time  during  the  Term,  the  method  of  taxation  prevailing  at the
Effective  Date shall be altered so that,  in  substitution  for ad valorem
real estate taxes, any new Imposition or charge, or any part thereof, shall be

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measured by or be based in whole or in part upon the Master Lease Property and
shall be imposed upon Landlord, then all such new  Impositions  or charges,
or any part  thereof,  shall be deemed to be included within the term
"Impositions",  and Tenant shall pay and discharge the same as herein provided
in respect of the payment of Impositions.

                  (e) (i) If permitted by  Applicable  Law, and provided no
Event of Default is then in existence,  Tenant shall have the right, at its
own expense, to contest the amount or validity, in whole or in part, of any
Imposition by appropriate  proceedings  diligently conducted in good faith.
If, under  Applicable  Law, the  contested  Imposition  must be paid before
undertaking the contest,  Tenant shall pay such  Imposition  (which payment
may be made under protest, at Tenant's option) or, if permitted by Landlord
and any mortgagee of Landlord (including trustees or beneficiaries of deeds
of trust)  ("Mortgagee"),  either deposit with  Landlord,  Mortgagee or the
assessing  body, as Landlord,  Mortgagee or the assessing body may require,
an amount  sufficient  to pay all amounts  referred to in  Subsection  (ii)
below,  or undertake such other method of securing  payment of such amounts
as is satisfactory to Landlord, Mortgagee and the assessing body.
                      (ii)     Upon the termination of any such proceeding,
Tenant shall pay the amount of such  Imposition  or part thereof as finally
determined as due in such  proceedings,  the payment of which may have been
deferred  during the  prosecution  of such  proceedings,  together with any
costs,  fees,  interest,  penalties  or  other  liabilities  in  connection
therewith,  and, upon such payment,  Landlord  shall,  provided an Event of
Default is not then in existence, return or request Mortgagee to return any
amount still on deposit with it or with Mortgagee with respect to such paid
Imposition.  If at any time  during  the  continuance  of such  proceedings
Landlord,  Mortgagee or the assessing body shall deem the amount  deposited
or the undertaking insufficient,  Tenant shall, upon thirty (30) days prior
written  notice,  make an additional  undertaking or deposit with Landlord,
Mortgagee or the assessing  body, as Landlord or Mortgagee  reasonably  may
request,  or as the assessing body may require,  and upon failure of Tenant
to do so, the amount  theretofore  deposited  shall be applied by Landlord,
Mortgagee or the  assessing  body to the payment,  removal and discharge of
such Imposition and the interest and penalties in connection  therewith and
any costs, fees (including, without limitation,  reasonable attorneys' fees
and  disbursements) or other liabilities  accruing in any such proceedings,
and the balance, if any, shall be returned to Tenant, or the deficiency, if
any, shall be paid by Tenant immediately on demand of Landlord or Mortgagee
to  the  taxing  authority  to  which  such  Imposition  is  payable.  This
subsection shall survive termination of this Lease.

                  (f)  Landlord  or  Tenant  may,  if it shall  so  desire,
endeavor  at any  time or  times  to  obtain  a  lowering  of the  assessed
valuation  upon the Master Lease  Property,  or any part  thereof,  for the
purpose of reducing Impositions thereon, and in such event, the other party


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will reasonably cooperate in effecting such reduction, but shall not be 
required to incur any out-of-pocket costs in so cooperating.

                  (g)  Landlord  shall  not  be  required  to  join  in any
proceedings  referred to in Subsection  (e) above unless the  provisions of
any law,  rule or  regulation at the time in effect shall require that such
proceedings  be brought by or in the name of  Landlord  or any owner of the
Master  Lease  Property,  in  which  event,  Landlord  shall  join  in such
proceedings or permit the same to be brought in its name and shall sign all
documents reasonably necessary to prosecute the proceedings. Landlord shall
not be subject to any liability for the payment of any costs or expenses in
connection  with any such  proceedings,  and Tenant will indemnify and save
harmless Landlord from and against any such costs and expenses,  including,
but not limited to, reasonable attorneys' fees and disbursements,  and from
any  liability  resulting  from  such  proceeding.  After  reimbursing  and
indemnifying  Landlord for the items referred to in the preceding sentence,
Tenant shall be entitled to any refund with respect to any  Imposition  and
penalties  or  interest  thereon  which  have been paid by Tenant  (whether
directly or through  escrowed  funds),  or which have been paid by Landlord
but previously reimbursed in full to Landlord by Tenant.  Tenant's right to
the refund shall survive termination of this Lease.

                  (h) The certificate,  advice,  statements, or bill of the
appropriate  official  designated  by law to make or  issue  the same or to
receive  payment of any  Imposition  shall be prima facie evidence that the
Imposition  is due and unpaid at the time of the making or issuance of such
certificate, advice statement or bill.

                  (i)  Tenant  shall  make  all  payments  of   Impositions
directly to the appropriate governmental authorities, and Landlord appoints
Tenant  the  attorney-in-fact  of  Landlord  for the  purpose of making all
payments  to be made by Tenant  pursuant to any of the  provisions  of this
Lease to persons or  entities  other than  Landlord.  In case any person or
entity  to whom any sum is  directly  payable  by  Tenant  under any of the
provisions  of this  Section 7 shall  refuse to accept  payment of such sum
from Tenant,  Tenant shall  thereupon  give written  notice of such fact to
Landlord and shall pay such sum  directly to Landlord  and  Landlord  shall
promptly pay such sum to such person or entity.

                  (j) Tenant shall deliver to Landlord  duplicate  receipts
or photostatic copies thereof, or other evidence reasonably satisfactory to
Landlord  (followed by such duplicate  receipts or copies,  when available)
showing the payment of all Impositions, within ten (10) business days after
the  respective  payments  are  required to be made by Tenant and  Landlord
requests such evidence in writing.

                  (k)  Landlord  shall  furnish  to  Tenant  copies  of all
notices of assessment  and bills  relating to  Impositions  within ten (10)
business days after Landlord receives any of the same from the governmental
authorities.

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                  SECTION 8.        UTILITIES

                  (a) Tenant  agrees to pay all  charges  made  against the
Master  Lease  Property  for  gas,   heat,   water,   electricity,   sewage
disposition,  telephone and all other utilities and services related to the
Master Lease Property during the Term (collectively, the "Utilities").

                  (b) Tenant understands,  acknowledges and agrees that any
one or more of the Utilities may be  interrupted or diminished by reason of
causes  beyond  Landlord's  reasonable  control;  that  Landlord  does  not
represent or warrant the uninterrupted avail ability of the Utilities; that
Tenant shall be solely responsible for obtaining and maintaining the use of
the Utilities;  and that, unless caused by Landlord or its Agents, any such
interruption  or  diminishment  shall  not (i) be  deemed  an  eviction  or
disturbance  of  Tenant's  right to  possession,  occupancy  and use of the
Master Lease Property or any part thereof,  or (ii) render  Landlord liable
to Tenant in damages by abatement of Rent or otherwise,  or relieve  Tenant
from the obligation to perform its covenants  under this Lease. In pursuing
the  Development,  Landlord  shall  take and cause its  Agents to take best
efforts to avoid the interruption or diminishment of the Utilities.

                  SECTION 9.        SIGNS

                  (a) Tenant shall not  inscribe,  paint,  affix or display
any sign,  advertisement or notice (collectively "Signs") on any portion of
the Main  Building  Area (or on any interior  portion of the Main  Building
that is visible from the exterior) not presently  located  thereon  without
the  prior  written  consent  of  Landlord,  which  consent  shall  not  be
unreasonably withheld or delayed.

                  (b) Tenant shall not  inscribe,  paint,  affix or display
any  Sign on any  portion  of the  Unimproved  Area not  presently  located
thereon without the prior written consent of Landlord,  which consent shall
be in Landlord's  sole and absolute  discretion.  After a Triggering  Event
with respect to an Excluded  Area on which any Sign then  exists,  Landlord
shall have the right, at its sole expense, to remove such Sign. If any Sign
is to be removed pursuant to the preceding sentence, Landlord, if requested
by Tenant, shall relocate the Sign, and any lighting and electrical service
related to the Sign,  to another  location  reasonably  agreed  upon by the
parties and providing  substantially similar visibility to that afforded by
the prior location.

                  (c)  Despite  the  foregoing,  Tenant  shall not  require
Landlord's  consent to replace any Sign existing as of the  Effective  Date
provided that the dimensions and location of the new Sign are substantially
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                  SECTION 10.       AS-IS CONDITION OF MASTER LEASE PROPERTY

PRIOR TO THE EFFECTIVE DATE, TENANT OWNED THE LAND FOR APPROXIMATELY THIRTY
(30) YEARS,  DEVELOPED THE IMPROVEMENTS THEREON,  INCLUDING BUT NOT LIMITED
TO THE MAIN BUILDING,  AND OCCUPIED THE MAIN BUILDING.  CONSEQUENTLY,  UPON
THE EFFECTIVE  DATE,  TENANT SHALL ACCEPT THE MASTER LEASE  PROPERTY IN "AS
IS" CONDITION.  TENANT AGREES AND  ACKNOWLEDGES  THAT LANDLORD HAS NOT MADE
ANY  REPRESENTATION  RESPECTING  OR ANY  WARRANTY  WHATSOEVER,  EXPRESS  OR
IMPLIED,   REGARDING  THE  MASTER  LEASE   PROPERTY,   INCLUDING,   WITHOUT
LIMITATION,  REPRESENTATIONS OR WARRANTIES REGARDING THE PHYSICAL NATURE OR
CONDITION  OF THE MASTER LEASE  PROPERTY.  TENANT  ACKNOWLEDGES  THAT IT IS
COGNIZANT OF AND SATISFIED  WITH ALL ASPECTS OF THE MASTER LEASE  PROPERTY,
AND THAT AS PROVIDED HEREIN THIS TRANSACTION IS AN "AS IS" TRANSACTION.

                  SECTION 11.       REPAIRS, MAINTENANCE AND MANAGEMENT

                  (a) Tenant shall,  at its sole expense,  keep,  maintain,
manage and operate (collectively,  "Care" or "Care for" or "Care of" as the
context may require) the Main Building Area in good condition and repair in
a manner consistent with Care for Class B suburban buildings of similar age
and character and used for similar purposes in Montgomery County,  Maryland
("Comparable Buildings"), and in compliance with all Applicable Laws in all
material respects.  Except as otherwise  provided in Subsection  5(b)(iii),
Subsection  5(b)(iv)(A),  Subsection  5(b)(iv)(B),  Subsection 5(b)(iv)(C),
Subsection  5(b)(iv)(D),  Subsection 8(b),  Section 10,  Subsection  11(a),
Subsection  11(c),  Subsection  11(d),  Subsection  12(a),  Subsection  15,
Subsection 16(b),  Subsection 17(a)(i),  Subsection 17(a)(iii),  Subsection
17(b), Section 23, Subsection 27(b),  Subsection 27(f) of this Lease to the
contrary,  Tenant  shall make and perform  all  necessary  maintenance  and
repairs to the Main Building Area, whether  structural and  non-structural,
ordinary and extraordinary,  foreseen and unforeseen, of every nature, kind
and description.  All repairs made by Ten ant shall be reasonably suited to
accomplish  their  intended  purposes  and  shall  be  in  compliance  with
Applicable Laws in all material respects.  The necessity for or adequacy of
Care  shall  be  measured  by  the  standards  which  are  appropriate  for
Comparable  Buildings;  provided,  that Tenant  shall in any event make all
repairs  necessary to avoid structural damage to the Main Building or other
damage or injury to  persons,  property  and other  portions  of the Master
Lease  Property.  However,  Landlord shall be  responsible  for any repairs
necessitated by Landlord or its Agents.

                  (b) Tenant shall  further  Care for the  remainder of the
Master Lease  Property and keep the same in good  condition and repair in a
manner  consistent  with other similar  properties  in  Montgomery  County,
Maryland (the "Comparable  Properties") and in material compliance with all
Applicable Laws. All repairs made by Tenant shall be reasonably suitable to
accomplish  their  purposes  and  shall  be  in  material  compliance  with
Applicable Laws. Tenant shall in any event make all repairs necessary to

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avoid structural damage to the improvements or other damage or injury to
persons, property and other portions of the Master Lease  Property.  However,
Landlord shall be  responsible  for any repairs necessitated by Landlord or its
Agents. Further, Tenant, while it was owner of the  Property,  recorded a
Declaration  of  Easements,  Covenants,  and Restrictions (the  "Declaration")
which, among other things,  sets forth a standard of Care for the Master Lease
Property.  Landlord hereby  delegates to Tenant,  and Tenant hereby accepts
from Landlord,  the  maintenance  and repair obligations applicable to the
Master Lease Property and described in Section 6 of the Declaration.

                  (c) If any  dispute  shall  arise  between  Landlord  and
Tenant as to the  standard of Care  required  under  Subsection  (a) or (b)
above,  the matter shall be resolved by binding  arbitration  in accordance
with the  then  prevailing  Commercial  Arbitration  Rules of the  American
Arbitration  Association (the "AAA"). Upon demand for arbitration by either
party in  accordance  with such  rules,  the  matter  shall be decided by a
single arbitrator in Montgomery  County,  Maryland,  selected in accordance
with the prevailing  Commercial  Arbitration  Rules of the AAA. In deciding
any matter  relating to the Main Building Area,  the arbitrator  shall take
into account the age and character of the Main  Building,  the standards of
Care set forth in this  Section 11, and the  remaining  Term of this Lease.
The arbitrator  shall hold a hearing on the matter within  forty-five  (45)
days after he or she is  appointed.  At least  twenty  (20) days before the
hearing,  each party shall submit to the other party a written statement of
its case,  copies of all  documents  upon  which it  intends to rely at the
hearing,  and a list of the  witnesses it intends to call to testify at the
hearing.  The hearing shall be concluded within fifteen (15) days after the
initial  hearing date and the  arbitrator  shall  decide the matter  within
fifteen  (15) days after the hearing is  concluded.  The  arbitrator  shall
render his or her  decision in writing,  setting  forth the reasons for the
decision.  Each party shall bear its own costs related to the  arbitration,
except that the parties shall share equally all filing fees and other costs
imposed by the AAA in connection  with the  arbitration and the fees of the
arbitrator.   The   decision   of  the   arbitrator   shall  be  final  and
non-appealable  and judgment on the decision may be entered in any court of
competent jurisdiction.

                  (d)  Notwithstanding  Subsections  (a)  and  (b),  unless
required by Applicable  Laws,  Tenant shall not be required to (i) improve,
upgrade,  re-model,  retrofit,  or  renovate  all or any  part of the  Main
Building  Area  or  (ii)  make  any  replacement  or  major  repair  of any
component,  element or system of the Main  Building Area where a more minor
repair may be  sufficient  to allow the ordinary  use and  occupancy of the
Main Building Area.

                  (e) In addition to the Care  required by this Section 11,
Tenant, at its sole expense, within five (5) years after the Effective Date
(subject to extension for Unavoidable Delays), shall complete the work (the
"Roof Work") described in Exhibit F attached hereto and made a part hereof.

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                  (f)  Landlord  agrees that during the Term,  Tenant shall
have the right,  after  providing  prior  written  notice to  Landlord,  to
enforce any rights of Landlord  under  applicable  warranties,  guarantees,
licenses and permits  applicable to the Main Building Area.  Landlord shall
sign such  documents  and  otherwise  reasonably  cooperate  with Tenant to
facilitate such  enforcement,  provided that Landlord shall not be required
to incur any out of pocket expense to third parties in so doing.

                  SECTION 12.       ACCESS TO MASTER LEASE PROPERTY

                  (a) Tenant  acknowledges  that Landlord has a significant
economic  interest in the Care of the Main Building Area and that Landlord,
pursuant  thereto,  has a need,  from  time to time,  to  inspect  the Main
Building  Area to insure  Tenant's  conformity  with the  covenants of this
Lease.  Tenant,  therefore,  hereby  authorizes  Landlord  and any  parties
authorized  by Landlord to perform such  inspections  of the Main  Building
Area as  Landlord  from  time  to time  may  reasonably  deem  appropriate.
Landlord  shall have the right to enter any part of the Main  Building Area
at all  reasonable  times,  upon  reasonable  advance  notice to Tenant and
accompanied by a representative of Tenant,  for the purposes of making such
inspections,  showing the Main  Building  Area to  prospective  purchasers,
investors,  mortgagees and tenants, and making such repairs, alterations or
improvements  to the Main Building  Area as Landlord may deem  necessary or
desirable  if Tenant  fails to  properly  Care for same  after  notice  and
opportunity to cure as provided for in Section  21(a).  No such entry shall
materially  interfere  with the use and occupancy of the Main Building Area
by Tenant, its subtenants and licensees.  Landlord shall incur no liability
to Tenant for such entry  except in the case of death,  bodily  injury,  or
property  damage  caused by  Landlord or its  Agents.  Notwithstanding  the
foregoing, Landlord shall have no right to enter upon those portions of the
Main  Building  which  are  secured  or  confidential   areas  pursuant  to
Applicable  Laws or  agreements  to which  Tenant is  subject  ("Restricted
Areas").  Further,  no person who is a foreign  national may enter into the
Main  Building  on behalf of  Landlord,  unless  approval of such person is
obtained from Tenant in advance.  Such approval may be withheld only to the
extent entry by such person would violate  Applicable Laws or agreements to
which Tenant is subject.

                  (b)  Tenant  also   acknowledges   that  Landlord  has  a
significant  economic  interest in the Care of the Unimproved  Area, and an
on-going need to access the Unimproved Area in connection with Development.
Tenant, therefore, hereby authorizes Landlord and any parties authorized by
Landlord to enter upon the  Unimproved  Area at any time without notice and
without being  accompanied by a representative  of Tenant,  to perform such
inspections  of the  Unimproved  Area as  Landlord  from  time to time  may
reasonably deem  appropriate,  and further to perform  whatever  activities
Landlord  deems  necessary or  desirable,  in its sole  discretion,  to aid
Development,  provided  that such  activities do not amount to a Triggering
Event. Additionally, Tenant

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authorizes  Landlord  and any  parties  authorized  by  Landlord to use and
maintain  such  then  existing  roads  and  other   infrastructure  in  the
Unimproved Area, and to grant such easements and rights of way with respect
to the  Unimproved  Area as Landlord deems  necessary or desirable,  in its
sole  discretion.  However,  Landlord's  exercise of its rights  under this
Subsection 12(b) shall not materially  interfere with the use of, or access
to, the Unimproved  Area or the Main Building Area by Tenant or its Agents.
No development or construction work shall take place in the Unimproved Area
unless such Unimproved Area is first excluded from this Lease in accordance
with Section 6.

                  SECTION 13.       ALTERATIONS AND PERSONAL PROPERTY

                  (a) Except as required by Tenant's repair and maintenance
obligations  under  this  Lease,  Tenant  shall  not make any  alterations,
additions,  installations  or  other  improvements  ("Alterations")  to the
Master Lease Property or any part thereof without the prior written consent
of Landlord,  which consent shall not be  unreasonably  withheld or delayed
with  respect  to the Main  Building  Areas but which  may be  withheld  in
Landlord's sole discretion  with respect to the Unimproved  Area.  However,
nothing in this Section shall be deemed to diminish  Landlord's  obligation
to grant  easements  under Section 6(e) or Tenant's  right to replace Signs
under Section 9(d). Moreover,  Tenant need not seek the consent of Landlord
to (i) install any Alteration in the Main Building Area costing One Hundred
Seventy  Thousand  Dollars  ($170,000.00)  or less, (ii) install any tenant
improvement  work for subleased  space in the Main Building,  (iii) install
communications  equipment on the roof of the Main Building (the "Roof Based
Facilities") (provided any such piece of the Roof Based Facilities does not
exceed  twenty (20) feet in  diameter),  or (iv)  dismantle  and remove any
clean  room  contained  in the Main  Building  (collectively,  "Preapproved
Alterations"). Notwithstanding anything to the contrary herein, in no event
shall  Tenant make any  Alterations  which would  affect the  structure  or
structural  integrity  of the  Main  Building  or the  facade  of the  Main
Building or construct or place any communications equipment on the exterior
of the Main Building or other  exterior  portions of the Main Building Area
(except the Roof Based Facilities  described in clause (iii) above) without
obtaining the prior written consent of Landlord, which consent shall not be
unreasonably  withheld or delayed. Any Alteration in or to the Master Lease
Property,  whether or not  requiring  the  approval of  Landlord,  shall be
subject, however, in all cases to the following:

                      (i)     Except to the extent that any Alteration is a
Preapproved  Alteration,  no  Alteration  shall be made without at least 30
days prior notice to Landlord (unless  Applicable Laws require otherwise or
except  in the case of an  emergency,  in which  case,  Tenant  shall  give
Landlord as much notice as is  practicable),  accompanied  by a copy of the
proposed  plans and  specifications  in detail  reasonably  sufficient  for
Landlord to review same, the identity of the contractor and any

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subcontractors, and a copy of all contracts with respect to the Alteration.
All  Alterations  shall be made  promptly  at the sole cost and  expense of
Tenant and in a good and workmanlike manner and in material compliance with
all Applicable Laws. Tenant shall promptly  reimburse Landlord upon demand,
up to One Thousand  Dollars  ($1,000) in each instance,  for any reasonable
costs and expenses incurred by Landlord to third parties in connection with
Landlord's  review  of  Tenant's  proposed  plans  and  specifications,  or
revisions thereof  (collectively,  the "Plans");  provided,  however,  that
Tenant shall not be obligated to reimburse  Landlord for Landlord's  review
of any Plans in connection with Restoration  (except as provided in Section
15). Upon the request of Landlord,  but not more than once each Lease Year,
Tenant shall provide  Landlord with a written  description  of  Alterations
made to the Master Lease Property  since the later of (i) the  Commencement
Date, and (ii) the date of the last such report. In addition,  Tenant shall
provide "CAD" drawings to Landlord showing the current configuration of the
Main Building,  including,  without limitation, any Alterations made to the
Master  Lease  Property.  Such  drawings  shall be  delivered  to  Landlord
approximately twenty-four (24) months before the Expiration Date and within
thirty (30) days after the expiration or earlier termination of this Lease.

                      (ii)     The Master Lease Property at all times shall
be kept by Tenant free of liens for labor and materials supplied or claimed
to have been supplied to the Master Lease  Property in connection  with the
Alterations.

                      (iii)    Notice is hereby given that Landlord shall
not be  liable  for any  labor or  materials  furnished  to or for  Tenant.
Furthermore,  notice is  hereby  given to Tenant  and  Tenant's  mechanics,
laborers and materialmen  with respect to the Master Lease Property that no
mechanic's,  materialman's  or laborer's lien shall attach to or affect the
reversion or other interest of Landlord in or to the Master Lease Property.

                      (iv)     No Alteration shall, when completed, be of
such a  character  as to  render  any  part of the  Master  Lease  Property
anything other than a complete, self-contained structural unit.

                      (v)      Worker's compensation, builder's risk and
general  liability  insurance with respect to the Alteration as required by
Section 14 shall be maintained by Tenant.

                      (vi)      All Alterations, other than roof-top
communications  equipment,  shall be the property of Landlord. Tenant shall
have  no  obligation  to  remove,  or  to  pay  for  the  removal  of,  any
Alterations, other than roof-top communications equipment, upon termination
of this Lease.

                  (b) All personal property, including, but not limited to,
trade fixtures,  furniture,  furnishings,  telephone  switching  equipment,
roof-top communications equipment, generators and

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uninterrupted  power supply equipment,  and moveable  equipment  ("Personal
Property")  owned by Tenant,  and all Restricted  Property,  upon or in the
Master Lease Property shall remain the property of Tenant,  or remain under
Tenant's  control,  and shall be removed  by  Tenant,  at its sole cost and
expense,  upon  termination  of this  Lease or  surrender  by Tenant of the
Master Lease Property to Landlord.  (The term "Personal  Property" does not
include Fixtures and Limited  Personal  Property as defined in the Purchase
and Sale  Agreement.)  If such  removal  shall  injure or damage the Master
Lease  Property,  Tenant  shall  repair  the  damage  at its sole  cost and
expense,  reasonable  wear and tear excepted.  If Tenant fails to so remove
and repair,  Landlord shall have the right to remove the Personal  Property
and Restricted Property and to dispose of the same and to repair the Master
Lease Property without  accountability to Tenant,  and at the sole cost and
expense of  Tenant.  The  "Restricted  Property"  shall  mean all  personal
property,  including, but not limited to documents and equipment, which are
required to be secured or kept confidential  pursuant to Applicable Laws or
agreements to which Tenant is subject. The Restricted Property shall at all
times,  both  during  and  after the Term,  be the sole  responsibility  of
Tenant.  Tenant  covenants and agrees that no Restricted  Property shall be
left in or upon the Master Lease Property  after  termination of this Lease
or surrender by Tenant of the Master Lease  Property to Landlord.  Upon the
expiration  or  earlier  termination  of this  Lease  (or,  in the  case of
Excluded  Areas,  at the time such areas are excluded from the Master Lease
Property) all right,  title and interest to any  underground  storage tanks
located in the Master Lease  Property  (or, in the case of Excluded  Areas,
located in such  Excluded  Areas)  shall  automatically  convey to Landlord
without the  requirement  that either party execute any other  documents to
effectuate the conveyance and shall become part of Landlord's property.

                   SECTION 14.      INSURANCE

                  (a) At all times during the Term, Tenant, at its own cost
and  expense,  shall carry and maintain  the  insurance  coverage set forth
below (the "Insurance"):

                           (i)   Hazard insurance covering the Master Lease
Property (including,  without limitation,  all Alterations now or hereafter
made to the Master Lease  Property)  under an "All Risks of Physical  Loss"
policy (an "All  Risks  Policy")  written  with full  replacement  coverage
("Replacement  Value"),  i.e., in an amount equal to 100% of the full costs
of  replacement  of the  insurable  portions of the Master Lease  Property,
excluding  foundation and excavation  costs and subject to such  reasonable
deductibles  as  Tenant  may see fit to carry  and as  Landlord  reasonably
approves.  For the  purposes  of this  Section  14,  deductibles  up to the
amounts stated on Schedule II attached hereto shall automatically be deemed
reasonable  deductibles  without  any need  for  Landlord's  approval.  The
insurer's   determination  of  Replacement   Value  shall  be  binding  and
conclusive on Landlord and Tenant. A stipulated value or agreed

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amount endorsement deleting the co-insurance  provision of the policy shall
be provided with such insurance.  If not otherwise  included within the All
Risks Policy specified above, Tenant shall carry or cause to be carried, by
endorsement  to such All Risks Policy,  coverage  against (i) damage due to
water and sprinkler leakage, with limits of coverage reasonably required by
Landlord,   and  (ii)  building   ordinance  covering  increased  costs  of
construction with a limit of not less than twenty-five percent (25%) of the
value of the Main  Building  Area and  demolition  with a limit of not less
than  ten  percent  (10%)  of the  value of the  Main  Building  Area.  The
Replacement Value shall include the cost of debris removal and the value of
grading,   paving  and  landscaping,   and   architects',   engineers'  and
development fees.  During the course of any Alteration,  Tenant shall carry
insurance in the form of a "Builder's  Risk" policy with respect thereto in
such amount as reasonably required by Landlord.

                  (ii) Commercial  liability  insurance with respect to the
Master Lease Property and the operations related thereto, whether conducted
on or off the Master Lease Property,  against  liability for death,  bodily
injury, and property damage (the "Liability Policy").  The Liability Policy
shall be on an occurrence basis and specifically shall include:

                              (A) Contractual liability to cover Tenant's
obligations to indemnify Landlord as required under this Lease; and

                              (B) Water damage and sprinkler  leakage legal
liability.

The  Liability  Policy shall be written for a combined  single limit of not
less than Ten Million Dollars ($10,000,000). Such limit shall be subject to
reasonable  increase  from  time to time  (but not  more  than  once  every
twenty-four   (24)  months)  in  accordance  with  the  limits  then  being
customarily  carried with respect to Comparable  Buildings  and  Comparable
Properties,  or operations  similar to those being  conducted on the Master
Lease  Property.  Tenant may satisfy the required  coverage  limits for the
Liability  Policy by carrying a combination of primary and excess liability
policies providing  aggregate coverage in at least the limits stated herein
for such policy.

                 (iii) Boiler and machinery insurance with limits as from time
to time customary for Comparable  Buildings and appropriate in the light of the
cost of repairing potential damage.

                 (iv)  Rent loss insurance ("Rent Insurance") on the "All Risks
of Physical  Loss" basis in an amount  equal to  twenty-four (24) months of
the then current Base Rent.

               (b)  Tenant further covenants and agrees, at its sole cost
and expense, to procure and maintain or cause to be procured and maintained
at all times all necessary worker's compensation

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insurance  covering all persons  employed by Tenant,  Existing  Tenants and
Subtenants in and about the Master Lease Property.

               (c)  Tenant further covenants and agrees, at its sole cost
and expense, to procure and maintain or cause to be procured and maintained
at  all  times  Comprehensive  Automobile  Insurance  covering  all  owned,
non-owned,  and hired  automobiles of tenant in limits of not less than One
Million Dollars ($1,000,000).

                (d)  In  addition  to the  insurance  carried  by  Tenant,
during the course of any Alteration or Care work undertaken by a contractor
hired by or for Tenant,  Tenant  shall  require  such  contractor  to carry
public  liability  insurance in limits of not less than Two Million Dollars
($2,000,000).

                (e)  Tenant  may  at its  option  provide  any  Insurance
coverage under a blanket  insurance  policy instead of a separate policy or
policies,  provided that the certificate or certificates  issued under such
blanket  insurance policy,  and the coverage afforded thereby,  conforms in
all respects to the requirements hereof (a "Blanket Policy").

                (f)  Tenant  acknowledges  that it currently carries flood
and  earthquake  coverage  ("Flood and Earthquake  Insurance").  Tenant not
shall not be required to maintain the Flood and Earthquake Insurance during
the Term;  provided,  however,  Tenant shall give  Landlord at least thirty
(30)  days  written  notice  prior to any  discontinuance  of the Flood and
Earthquake Insurance.  Notwithstanding the foregoing, (i) in the event that
any portion of the Property is classified as being located in (A) a Class A
flood  zone or any  other  flood  zone  indicating  a higher  frequency  of
predicted  flooding  than a Class A flood zone as  indicated by the Federal
Emergency  Management Agency (a "Flood Zone"), or (B) a B3 seismic activity
zone or any other seismic  activity zone  indicating a higher  frequency of
predicted  seismic activity than B3 seismic activity zone as indicated by a
consensus of  insurance  underwriters  that  underwrite  such  policies for
earthquake coverage (a "Seismic Activity Zone"), Tenant shall procure Flood
and  Earthquake  Insurance  if such  coverage is customary  for  Comparable
Buildings and Comparable Properties, or (ii) to the extent the Master Lease
Property is insured under a Blanket Policy and such Blanket Policy contains
Flood and  Earthquake  Insurance for any other  property under such Blanket
Policy,  Tenant shall maintain Flood and Earthquake  Coverage on the Master
Lease Property.

                (g)  All  Insurance,  except  for  Flood  and  Earthquake
Insurance  if the Property is not in Flood Zone or Seismic  Activity  Zone,
shall be in such form and shall be  issued  by such  responsible  insurance
companies  licensed  to do  business  in  the  State  of  Maryland  as  are
reasonably  approved by  Landlord.  Any  insurance  company  rated by Bests
Insurance Reports (or any successor  publication of comparable standing) as
"A-,  VIII" or  better  and by  Standard  &  Poor's  (or any  successor  of
comparable standing) as "A" or better (or the equivalent of such rating)

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(collectively, the "Standard Rating") shall be deemed a responsible company
and acceptable to Landlord.  Notwithstanding  the  foregoing,  in the event
that the rating of such  insurance  falls below the Standard  Rating during
the term of the policy of such  insurance,  Tenant shall not be required to
procure  replacement  coverage  until the  scheduled  expiration or earlier
termination  of such  policy;  provided,  however,  in no event  shall such
period exceed twelve (12) months.  Upon the Effective Date, and thereafter,
not less than five (5) days prior to the  expiration  dates of the expiring
policies  of  Insurance,  originals  of  replacement  policies  or  renewal
certificates,  as the case may be, bearing notations evidencing the payment
of premiums or  accompanied by other evidence  reasonably  satisfactory  to
Landlord  of each  payment,  shall  be  delivered  by  Tenant  to  Landlord
("Insurance  Notice").  If  Tenant  does  not  provide  Landlord  with  the
Insurance Notice or if Tenant lets any Insurance lapse, Landlord shall have
the right,  without providing any notice to Tenant, to procure  replacement
coverage  that is  effective  upon such  lapse and  Tenant  shall  promptly
reimburse Landlord for the reasonable cost thereof.

                  (h)  All  policies  of  Insurance  shall  name  Landlord,
Tenant,  and,  if  requested  by  Landlord in  writing,  any  Mortgagee  as
insureds,  as their  respective  interests  may  appear.  All  policies  of
Insurance other than the Liability Policy shall, if requested in writing by
Landlord,  name the  Mortgagee  as a loss  payee,  as the  interest of such
Mortgagee  may  appear,  but subject to the  provisions  of Section 15. Any
request of coverage as to a Mortgagee  shall set forth the name and address
of the Mortgagee.

                  (i) Tenant shall not violate or permit to be violated any
of the conditions,  provisions or requirements of any Insurance policy, and
Tenant shall  perform,  satisfy and comply with,  or cause to be performed,
satisfied and complied with, the conditions, provisions and requirements of
all Insurance  policies and the companies writing such policies so that, at
all  times,  the  Insurance  shall  be  provided  by  companies  reasonably
acceptable to Landlord, except as otherwise provided in Subsection 14(g).

                  (j) Each policy or certificate of Insurance shall contain
(i) an  agreement  by the insurer  that such policy  shall not be canceled,
modified or denied renewal  without at least thirty (30) days prior written
notice to  Landlord  and any  Mortgagee  named as an insured or loss payee,
except  that if the  reason  for  cancellation  or  denial  of  renewal  is
nonpayment of premiums, the notice will be at least ten (10) days, and (ii)
a waiver of subrogation by the insurer.

                  (k) If by  reason  of  changed  economic  conditions  the
Insurance  amounts  referred  to in  this  Lease  become  inadequate,  upon
Landlord's request, the limits shall be reasonably increased by Tenant from
time to time (but not more often than once every  twenty-four  (24) months)
to meet  the  changed  conditions,  but any  changes  in  limits  shall  be
consistent with what is customary for

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Comparable Buildings and Comparable Properties or for operations similar to
those conducted on the Master Lease Property.  Upon the reasonable  request
of  Landlord,  Tenant  shall  procure and obtain such types of insurance in
lieu of the current insurance then required under this Lease; provided that
such replacement coverage is of a substantially similar scope and nature as
the Insurance  then required  under this Lease and is the type of insurance
that is customary for Comparable Buildings and Comparable Properties or for
operations  similar  to  those  conducted  on the  Master  Lease  Property.
Notwithstanding  the  foregoing,  in the event  that  Landlord  makes  such
request  during  the  term of the  policy  of the  insurance  that is being
replaced,  Tenant  shall not be  required to procure  replacement  coverage
until the  scheduled  expiration  or earlier  termination  of such  policy;
provided, however, in no event shall such period exceed twelve (12) months.

                  (l)  Notwithstanding any provisions in this Section 14 or
elsewhere in this Lease to the  contrary,  any  deductible  to the All Risk
Policy shall be deemed an amount covered by Insurance and shall be promptly
paid by Tenant in the event of an Insurable Casualty.

         SECTION 15.       DAMAGE OR DESTRUCTION

                  (a) In case of damage  to or  destruction  of the  Master
Lease  Property or any part thereof by fire or other  casualty  ("Damage"),
Tenant will promptly give written notice thereof to Landlord. If the Damage
is caused by an Insurable  Casualty,  Tenant shall,  in accordance with the
provisions of this Section and all other provisions of this Lease,  restore
the same as nearly as possible to its condition  and character  immediately
prior to such  Damage,  subject to Tenant's  right to make  Alterations  in
substantial  conformity  with and subject to the  conditions  of Section 13
hereof, and in conformity with the plans and specifications  required to be
prepared pursuant to Section 13 and subject to any restrictions  imposed by
Applicable  Laws  ("Restoration"),  whether or not  insurance  proceeds are
sufficient to pay in full the cost of the work.  The  Restoration  shall be
commenced  within sixty (60) days after the loss is finally  adjusted  with
the insurer,  the plans,  specifications  and contract for the  Restoration
have been  approved by Landlord  under Section  15(b)(i) and (ii),  and all
necessary permits for the Restoration have been issued. Tenant shall pursue
such adjustment of the loss, approvals of Landlord, and issuance of permits
with  reasonable  diligence  after the  Damage.  The  Restoration  shall be
prosecuted and completed with reasonable  diligence after its commencement,
Unavoidable Delays excepted.  Landlord shall cooperate fully with Tenant in
order to obtain the largest possible  insurance  recovery and shall execute
any and all  consents  and other  instruments  and take all  other  actions
reasonably  necessary  to  accomplish  the same and to cause the  insurance
proceeds to be paid as provided in Subsection (c) below.


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                  (b) In the event that the cost of Restoration exceeds One
Hundred Seventy  Thousand Dollars  ($170,000),  Tenant agrees to furnish to
Landlord at least twenty (20) days before the
commencement of Restoration, the following:

                           (i) Complete plans and specifications for
Restoration  prepared  by a licensed  and  reputable  architect  reasonably
satisfactory to Landlord (the "Architect"),  which plans and specifications
shall meet with the  reasonable  approval of  Landlord,  together  with the
approval   thereof  by  all   governmental   authorities   then  exercising
jurisdiction  with regard to such work, and which plans and  specifications
shall be and become the sole and absolute property of Landlord in the event
that, for any reason, this Lease shall be terminated.

                           (ii)     A contract then customary in the trade with
(A) the Architect,  and (B) a reputable and responsible  general contractor
reasonably   approved  by  Landlord,   providing  for  the   completion  of
Restoration  in  accordance  with  said  plans  and  specifications,  which
contract shall meet with the reasonable approval of Landlord.

                           (iii) Assignment of the contract with the
Architect  and the general  contractor  so  furnished,  duly  executed  and
acknowledged by Tenant, the Architect and the general contractor,  by their
terms to be effective upon any termination of this Lease or upon Landlord's
re-entry upon the Master Lease Property  prior to the complete  performance
of such contracts.

                  (c) All insurance  proceeds  payable on account of Damage
shall be paid to Mortgagee  (provided  such  Mortgagee is an  Institutional
Mortgagee) or to a trustee  designated by Mortgagee  ("Insurance  Trustee")
and applied to the payment of the cost of  Restoration,  including the cost
of temporary  repairs or for the  protection  of the Master Lease  Property
pending  the   completion   of  permanent   work  pursuant  to  the  plans,
specifications and contracts (all of which temporary repairs, protection of
Master Lease  Property and permanent work shall be deemed to be part of the
Restoration). In the event of Damage in which the proceeds of insurance are
Five Hundred Thousand Dollars ($500,000.00) or less, such proceeds shall be
payable  directly to Tenant,  in trust,  to be applied to the  Restoration.
Such funds shall be used only for such purposes  until the  Restoration  is
completed and any excess  proceeds  shall be retained by Tenant for its own
account.  In the event of Damage in which the proceeds of insurance  exceed
Five  Hundred  Thousand  Dollars  ($500,000.00),  such  proceeds  shall  be
deposited  with  Mortgagee or with the  Insurance  Trustee in a bank in the
Washington  D.C.  metropolitan  area as  designated  by Landlord  and, upon
written  request of Tenant,  shall be paid out to Tenant  from time to time
(but no more  often  than once per  month) as  Restoration  progresses,  in
trust,  for the purposes of paying the cost of Restoration.  The receipt by
Landlord and its  Mortgagee of the following  are  conditions  precedent to
each payment of insurance proceeds by the Mortgagee or Insurance Trustee to
Tenant:

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                           (i)     A requisition ("Requisition") signed by
Tenant,  dated not more than 30 days prior to such request,  certifying the
following:

                                  (A)  that the sum then requested either has
been  paid by  Tenant  or is  justly  due to  contractors,  subcontractors,
materialmen,  engineers,  architects  or other  persons  who have  rendered
services or furnished  materials for the portion of the Restoration therein
specified, and giving a brief description of such services and material and
the  several  amounts  so paid or due to each of said  persons  in  respect
thereof,  and stating  that such  amounts  have not been the subject of any
previous  Requisition  and do not  exceed  the  value of the  services  and
materials described in the Requisition,  and stating, in reasonable detail,
the progress of the work in connection  with  Restoration up to the date of
the Requisition;

                                  (B)  that, to the best of Tenant's knowledge,
except  for the  amount  set forth in the  Requisition  and  except for any
amount  related to services or  materials  furnished  after the date of the
Requisition, there is no other amount then due for services or materials in
connection with Restoration  which, if unpaid,  might become the basis of a
mechanic's,  materialmen's,  or similar lien upon the Master Lease Property
or any part thereof; and

                                  (C)  that, to the best of Tenant's knowledge,
the materials,  fixtures and equipment for which payment is being requested
pursuant to this Section are substantially in accordance with the plans and
specifications approved by Landlord.

For the purposes of this Subsection 15(c)(i), (i) "Institutional Mortgagee"
shall mean Nomura Asset Capital  Corporation and its successors and assigns
or any federally insured savings bank,  federally insured  commercial bank,
trust company, life insurance company,  casualty insurance company, pension
fund, real estate investment trust, mortgage company, credit union, college
or university,  charitable  institution,  or government agency or fund with
tangible  net  worth  in  excess  of  Two  Hundred  Fifty  Million  Dollars
($250,000,000),  and (ii) "Tenant's  knowledge" shall mean the then current
knowledge of the General  Manager of  Corporate  Services of Tenant or such
other authorized representative of Tenant overseeing the Restoration.

                           (ii)    A certificate or report of a title insurance
company  reasonably  satisfactory to Landlord and such Mortgagee,  or other
evidence  reasonably  satisfactory to Landlord and such  Mortgagee,  to the
effect  that  there has not been filed  with  respect  to the Master  Lease
Property or any part thereof or upon Tenant's  leasehold  interest  therein
any  mechanic's,  materialman's  or other lien in respect of such  services
rendered or materials furnished which has not been discharged of record.

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                           (iii) A certificate from Tenant stating that, to
the best of Tenant's knowledge, no Event of Default then exists.

Simultaneously with receipt of the insurance proceeds, Tenant shall deliver
to Landlord and such  Mortgagee  acknowledgments  of payment and waivers of
lien from all vendors,  mechanics and laborers  receiving  payment,  to the
extent of the work performed through the date of the previous Requisition.

                  (d) If the insurance  proceeds shall be  insufficient  to
pay the entire cost of Restoration, Tenant will pay the deficiency.

                  (e) Upon  receipt by  Landlord or any such  Mortgagee  of
satisfactory  evidence of the character  required by  Subsection  (c) above
that  Restoration  has been  completed  and  paid  for in full  (including,
without  limitation,  a copy of the permanent or temporary  certificate  of
occupancy for the Main Building,  if a new  certificate is issued or if the
then existing certificate is modified, and a then current,  complete set of
"as built" plans for the Restoration,  if the cost of such plans is covered
by  Insurance)  and that there are no Events of Default then in  existence,
any balance of the insurance  proceeds at the time held by Mortgagee or the
Insurance  Trustee  shall be paid to and may be  retained by Tenant for its
own account.

                  (f) Notwithstanding the foregoing,  if at the time of any
Damage,  Tenant fails to maintain a credit  rating for  Tenant's  corporate
debt of at least BB as rated by an "Approved  Credit  Rating  Agency",  the
following provisions shall apply:

                           (i)  All references in Subsection 15(c) to "Five
Hundred Thousand  Dollars  ($500,000)"  shall be deemed  references to "One
Hundred Thousand Dollars ($100,000)";

                           (ii)   The   following   shall   be   additional
conditions precedent  to those set forth in  Subsection  15(c) in order for
Tenant to receive insurance proceeds held by the Mortgagee or Insurance Trustee:

                                    (A) A Certificate from the Architect
stating that the  materials,  fixtures  and  equipment  for which  payment is
being requested pursuant to this Section are substantially in accordance with
the plans and specifications approved by the Landlord.

                                    (B) Upon  occurrence of Damage,  Tenant
shall deposit with Mortgagee or the Insurance  Trustee any  deductible  under
the Insurance.  In  addition,  Tenant  shall  deposit  with the  Mortgagee  and
Insurance Trustee any excess cost of the  Restoration  over the  Insurance
Proceeds and Deductible held by Landlord at the time of final adjustment of
the loss or at the time of any Requisition.

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                                    (C) Ten percent (10%) of the cost of the
Restoration  shall be held back by Mortgagee or the Insurance Trustee until
Tenant has complied with all of the provisions of this Section 15.

For purposes of this Subsection  15(f), an "Approved  Credit Rating Agency"
shall mean Standard & Poor's,  Moody's or any other  nationally  recognized
rating agency.

                  (g)  If any  Damage  shall  occur,  then,  to the  extent
Landlord  is  compensated  by  the  Rent  Insurance   required  by  Section
14(a)(iv),  Base Rent shall  abate from the date of the  Damage,  until the
date the Restoration is completed,  to the extent that the Main Building is
rendered unusable by the Damage.

                  (h) Despite the foregoing, if (i) Damage in excess of TWO
MILLION FIVE HUNDRED THOUSAND AND NO/100 DOLLARS  ($2,500,000) or in excess
of an amount  equal to the  remaining  payments of Base Rent due under this
Lease, whichever is less, is caused by a casualty which is not an Insurable
Casualty,  or (ii) during the last two (2) Lease Years of the Term,  Damage
is caused by an  Insurable  Casualty  and the loss  amounts to  twenty-five
percent (25%) or more of the Replacement Value of the Main Building,  then,
in either  event,  Tenant shall have the right to  terminate  this Lease by
giving written  notice of  termination to Landlord  within ninety (90) days
after  the  occurrence  of such  Damage  provided  that the Rent  Insurance
required  by  Section  14(a)(iv)  is then in  effect.  In the event of such
termination,  the Term of this Lease shall expire and come to an end thirty
(30) days  after the day that the  notice is given  with the same force and
effect  as if that  day had  been the  Expiration  Date  and any  insurance
proceeds  payable  for the Damage  shall  exclusively  belong to  Landlord.
Thereafter,  neither  party  shall have any further  rights or  liabilities
under this Lease,  except with  respect to any  obligations  which arose or
accrued before the termination or with respect to any rights or liabilities
which expressly survive  termination under the terms of this Lease. As used
in this Lease  "Insurable  Casualty" means any casualty,  regardless of the
degree of the  Damage,  covered by  Insurance  which  Tenant is required to
maintain under Section 14, whether or not Tenant  maintains such insurance.
Notwithstanding any other provision contained in this Section, Tenant shall
not be entitled to terminate  this Lease (A) if the Damage is caused by (i)
any  fraudulent or dishonest act or acts  committed by the Tenant or any of
the Tenant's  employees with the manifest intent to (a) cause the Tenant to
sustain such loss and (b) obtain financial benefit for the Tenant, Tenant's
employee, or for any other person or organization intended by the Tenant or
the  Tenant's  employee  to receive  such  benefit  (other  than  salaries,
commissions,  fees, bonuses, promotions,  awards, profit sharing, pensions,
or other employee  benefits earned in the normal course of employment),  or
(ii)  the  risks of  contraband  or  illegal  trade,  or  (iii)  any of the
following:  (1) defective design or  specifications,  faulty  material,  or
faulty workmanship;  (2) mechanical breakdown;  (3) ordinary wear and tear,
gradual deterioration, insect, vermin, inherent vice and loss of use; (4)

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normal settling or shrinkage of walls, floors, or ceilings;  or (5) loss of
market,  business  interruption,  or extra  expense  loss due to delay with
respect to  property  in  transit;  or (B) in the case of clause (i) of the
first sentence of this Subsection 15(h), if Landlord provides the funds, in
excess of the applicable amount set forth in such clause (i),  necessary to
cause  Restoration of the Main Building,  in which event such funds will be
applied in the manner  provided in Subsection  15(c), as if such funds were
insurance proceeds.

                  (i) Notwithstanding any other provision contained in this
Section,  all  insurance  proceeds  payable  for loss or damage to Tenant's
Personal  Property shall be the exclusive  property of and be paid directly
to Tenant.

                  (j) Tenant hereby  releases  Landlord and Landlord hereby
releases  Tenant from any and all liability for any loss,  damage or injury
to person or  property  occurring  in,  on,  about or to the  Master  Lease
Property,  the Main  Building  Area or  personal  property  within the Main
Building Area, by reason of fire or other casualty,  to the extent proceeds
of Insurance are received for such loss, damage, or injury or to the extent
such proceeds  should have been  received  under  Insurance  required to be
carried by this  Lease.  Because the  provisions  of this  Subsection  will
preclude the assignment of any claim mentioned herein by way of subrogation
or otherwise to an insurance company or any other person, Tenant shall give
to each  insurance  company  which has issued to it one or more policies of
insurance, notice of the terms of the release contained in this Subsection,
and have such  insurance  policies  properly  endorsed,  if  necessary,  to
prevent the  invalidation  of insurance  coverages by reason of the release
contained in this Subsection.

                  SECTION 16.       INDEMNIFICATION

                  (a) Tenant  will  protect,  indemnify  and save  harmless
Landlord from and against all liabilities,  obligations,  claims,  damages,
penalties,   causes  of  action,  costs  and  expenses  (including  without
limitation,  reasonable  attorneys'  fees  and  expenses)  imposed  upon or
incurred by or asserted  against  Land lord by reason of (i) any  accident,
injury to or death of persons or loss of or damage to property occurring on
or about  the  Master  Lease  Property  or any part  thereof  caused by the
negligence  or  intentional  misconduct  of Tenant or its Agents;  (ii) any
failure on the part of Tenant to perform or comply with any of the terms of
this Lease; or (iii) performance of any labor or services or the furnishing
of any materials or other  property in respect of the Master Lease Property
or any part thereof at the  direction  of Tenant.  Tenant  hereby  releases
Landlord from any and all liability for the same.

                  (b) Landlord  will  protect,  indemnify and save harmless
Tenant from and  against all  liabilities,  obligations,  claims,  damages,
penalties,   causes  of  action,  costs  and  expenses  (including  without
limitation, reasonable attorneys' fees and

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expenses)  imposed upon or incurred by or asserted against Tenant by reason
of (i) any accident,  injury to or death of persons or loss of or damage to
property  occurring  on or about  the  Master  Lease  Property  or any part
thereof,  caused by the negligence or intentional misconduct of Landlord or
its  Agents;  (ii) any failure on the part of Landlord to perform or comply
with any of the terms of this Lease;  or (iii)  performance of any labor or
services or the furnishing of any materials or other property in respect of
the Master Lease Property or any part thereof at the direction of Landlord.
Landlord hereby releases Tenant from any and all liability for the same.

                  (c) The amount which any party (an "Indemnifying  Party")
is or may be required to pay to any other party (an "Indemnitee")  pursuant
to this  Section  16  shall  be  reduced  (including,  without  limitation,
retroactively)  by any  insurance  proceeds  (or the  amount  of  insurance
proceeds  that would have been  recovered  had  insurance  required by this
Lease been obtained) or other amounts actually recovered by or on behalf of
such  Indemnitee,  in reduction of the related loss. If an Indemnitee shall
have received payment (an "Indemnity  Payment") required by this Lease from
an  Indemnifying  Party  in  respect  of any loss  and  shall  subsequently
actually  receive  insurance  proceeds or other  amounts in respect to such
loss, then such Indemnitee shall pay to such Indemnifying Party a sum equal
to the amount of such insurance proceeds or other amounts actually received
(up to but not in  excess  of the  amount  of any  Indemnity  Payment  made
hereunder).  An insurer who would  otherwise  be obligated to pay any claim
shall not be relieved  of the  responsibility  with  respect  thereto,  or,
solely  by  virtue  of the  indemnification  provisions  hereof,  have  any
subrogation rights with respect thereto, it being expressly  understood and
agreed  no  insurer  or any  other  third  party  shall  be  entitled  to a
"windfall"  (i.e.,  a benefit  they would not be entitled to receive in the
absence of the indemnification provisions) by virtue of the indemnification
provisions hereof.

                  (d) Procedures for  indemnification of Third Party Claims
shall be as follows:

                           (i)      If an Indemnitee shall receive notice or
otherwise  learn  of  the  assertion  by  a  person   (including,   without
limitation, any governmental entity) who is not a party to this Lease (or a
subsidiary an affiliate of either party) of a claim or of the  commencement
by any such person of any action (a "Third  Party  Claim")  with respect to
which an  Indemnifying  Party may be obligated  to provide  indemnification
pursuant  to this  Section  16 or any other  Section  of this  Lease,  such
Indemnitee  shall  give such  Indemnifying  Party  written  notice  thereof
promptly after becoming aware of such Third Party Claim;  provided that the
failure of any  Indemnitee to give notice as provided in this Section 16(d)
shall not  relieve the  Indemnifying  Party of its  obligations  hereunder,
except to the extent that such Indemnifying Party is actually prejudiced by
such failure to give

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notice.  Such notice shall describe the Third Party Claim in
reasonable detail.

                           (ii) An  Indemnifying  Party may elect to defend
or to seek to settle or compromise,  at such Indemnifying  Party's own expense
and such  Indemnifying  Party's  own  counsel,  any Third Party  Claim,  as
provided hereafter. Within thirty (30) days after receipt of notice from an
Indemnitee in accordance with Subsection 16(d)(i) (or sooner, if the nature
of such Third Party Claim so requires), the Indemnifying Party shall notify
the Indemnitee of its election whether the  Indemnifying  Party will assume
responsibility  for defending such Third Party Claim.  After notice from an
Indemnifying  Party to an  Indemnitee of its election to assume the defense
of a Third Party Claim, such Indemnifying Party shall not be liable to such
Indemnitee  under this Section 16 for any legal or other  expenses  (except
expenses  approved  in  advance  by the  Indemnifying  Party)  subsequently
incurred  by such  Indemnitee  in  connection  with  the  defense  thereof;
provided that if the defendants  with respect to any such Third Party Claim
include both the Indemnifying  Party and one or more Indemnitees and in any
Indemnitee's reasonable judgment a conflict of interest between one or more
of such Indemnitees and such  Indemnifying  Party exists in respect to such
claim,  such Indemnitees shall have the right to employ separate counsel to
represent  such  Indemnitees  and in that  event  the  reasonable  fees and
expenses of such separate  counsel (but not more than one separate  counsel
reasonably  satisfactory to the  Indemnifying  Party) shall be paid by such
Indemnifying   Party.  If  an  Indemnifying  Party  elects  not  to  assume
responsibility  for  defending a Third Party  Claim,  or fails to notify an
Indemnitee of its election as provided in this Subsection  16(d)(ii),  such
Indemnitee  may defend  or,  subject to the  remainder  of this  Subsection
16(d)(ii),  seek to  compromise  or settle such Third  Party Claim  without
prejudice  to  such  Indemnitee's  rights,  if  any,  to  continue  to seek
indemnification  hereunder.   Notwithstanding  the  foregoing,  neither  an
Indemnifying  Party nor an Indemnitee  may settle or  compromise  any claim
over the  objection  of the  other;  provided,  however,  that  consent  to
settlement or  compromise  shall not be  unreasonably  withheld or delayed.
Neither an Indemnifying  Party nor an Indemnitee  shall consent to entry of
any  judgment or enter into any  settlement  of any Third Party Claim which
does not include as an unconditional  term thereof the giving by a claimant
or plaintiff to such Indemnitee,  in the case of a consent or settlement by
an  Indemnifying  Party,  or to the  Indemnifying  Party,  in the case of a
consent or  settlement  by an  Indemnitee,  of a written  release  from all
liability in respect to such Third Party Claim.

                           (iii) If an Indemnifying Party chooses to defend
or to seek to  compromise  or settle any Third  Party  Claim,  the  related
Indemnitee shall make reasonably  available to such Indemnifying  Party any
personnel or any books,  records or other  documents  within its control or
which it otherwise has the ability to make  available that are necessary or
appropriate for such defense, settlement or compromise of such Third Party

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Claims,   subject   to  the   establishment   of   reasonably   appropriate
confidentiality  arrangements  and  arrangements to preserve any applicable
privilege (including, the attorney-client privilege) and shall cooperate in
such defense, compromise or settlement. If an Indemnifying Party chooses to
defend or to seek to  compromise  or  settle  any Third  Party  Claim,  the
related  Indemnitee shall be entitled to attend and participate in any such
proceeding, discussion or negotiation at its own expense.

                           (iv)  Notwithstanding anything else in this
Section 16 to the contrary,  if an Indemnifying  Party notifies the related
Indemnitee  in writing  of such  Indemnifying  Party's  desire to settle or
compromise  a Third  Party  Claim on the  basis  set  forth in such  notice
(provided that such settlement or compromise  includes as an  unconditional
term thereof the giving by the  claimant or plaintiff of a written  release
of the  Indemnitee  from all  liability  in  respect  thereof  and does not
include any  non-monetary  remedy) and provides the  Indemnitee a copy of a
written  proposal of the applicable  claimant to settle on such terms,  and
the Indemnitee  notifies the Indemnifying  Party in writing within ten (10)
business  days of such notice that such  Indemnitee  declines to accept any
such settlement or compromise, such Indemnitee may continue to contest such
Third Party Claim, free of any participation by such Indemnifying Party, at
such  Indemnitee's  sole  expense.  In such event,  the  obligation of such
Indemnifying  Party to such  Indemnitee  with  respect to such Third  Party
Claim shall be equal to (i) the costs and expenses of such Indemnitee prior
to the date such  Indemnifying  Party notifies such Indemnitee of the offer
to settle  or  compromise  (to the  extent  such  costs  and  expenses  are
otherwise  indemnifiable  hereunder) plus (ii) the lesser of (A) the amount
of any offer of settlement or compromise which such Indemnitee  declined to
accept and (B) the actual out-of-pocket amount such Indemnitee is obligated
to pay subsequent to such date as a result of such Indemnitee's  continuing
to defend such Third Party Claim (including attorneys fees and expenses).

                          (v)   Any claim on account of a loss which does not
result from a Third Party Claim shall be asserted by written  notice  given
by the  Indemnitee to the related  Indemnifying  Party.  Such  Indemnifying
Party  shall  have a period of 30 days  after the  receipt  of such  notice
within  which to  respond  thereto.  If such  Indemnifying  Party  does not
respond within such thirty (30) day period,  such Indemnifying  Party shall
be deemed to have refused to accept responsibility to make payment. If such
Indemnifying  Party does not respond  within such thirty (30) day period or
rejects such claim in whole or in part,  such  Indemnitee  shall follow the
dispute resolution procedures set forth in Subsection 11(c).

                          (vi)   In addition to any adjustments required
pursuant to Subsection  16(c), if the amount of any loss shall, at any time
subsequent to the payment  required by this Lease,  be reduced by recovery,
settlement or otherwise,  the amount of such  reduction,  less any expenses
incurred in connection therewith,

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shall promptly be repaid by the Indemnitee to the Indemnifying Party.

                           (vii)  In the event of payment by an Indemnifying
Party to any  Indemnitee  in  connection  with any Third Party Claim,  such
Indemnifying  Party shall be subrogated to and shall stand in the place and
the place of such Indemnitee as to any events or  circumstances  in respect
of which such Indemnitee may have any right or claim relating to such Third
Party Claim  against any claimant or plaintiff  asserting  such Third Party
Claim or against any other person.  Such  Indemnitee  shall  cooperate with
such Indemnifying Party in a reasonable manner, and at the cost and expense
of such Indemnifying Party, in prosecuting any subrogated right or claim.

                           (vii) If any indemnity payment required to be made
hereunder is denominated  in a currency  other than United States  dollars,
such payment shall be made in United States  dollars and the amount thereof
shall be  computed  using  the  foreign  exchange  rate  for such  currency
determined  as of the date that  notice of the claim with  respect to which
such indemnity payment is made or given by, or on behalf of, the Indemnitee
to the Indemnifying Party.

                  (e) The provisions of this Section 16 shall survive any
termination of this Lease.

                  SECTION 17.       CONDEMNATION

                  (a) (i) If any part of the Master Lease Property is taken
or  condemned  for a  public  or  quasi-public  use  (a  sale  in  lieu  of
condemnation to be deemed a taking or condemnation) ("Taken" or a "Taking",
as the context  shall  require),  this Lease  shall,  as to the part Taken,
terminate as of the date title shall vest in the  condemnor and continue in
full force as to the remainder. In the event of such a partial Taking, Rent
shall be equitably  adjusted by Landlord and Tenant taking into account the
portion of the Master Lease Property so Taken;  provided,  that there shall
be no  adjustment  in Base Rent  unless,  and only to the  extent  that,  a
portion of the Main Building is Taken.  With respect to any other  portions
of the Master Lease Property  Taken,  adjustment  shall be made only to the
Additional  Rent applicable to and the obligation to Care for such portion.
Tenant, at its cost and expense, shall proceed with Restoration, subject to
Unavoidable  Delays,  of the remaining portion of the Master Lease Property
to  a  complete   architectural   unit,  to  the  extent   practicable  and
economically  feasible  and to the  extent  the net  condemnation  award is
sufficient to pay in full the cost of such  Restoration.  Such  Restoration
shall be performed  in the same manner and pursuant to the same  conditions
as set forth in Section 15 hereof with respect to  Restoration  as a result
of  Damage.  If the  parties  cannot  agree  upon such Rent  adjustment  or
Restoration  requirements,   such  dispute  shall  be  decided  by  binding
arbitration comparable to that provided for in Section 11(c).

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                          (ii) Tenant waives all claims against Landlord and
any  Mortgagee by reason of any partial  Taking,  and Tenant  covenants and
agrees that Tenant will make no claim against the  condemning  authority by
reason of the  partial  Taking,  except for  damages  payable for injury to
Personal Property or any Alterations that Tenant is entitled to remove upon
the expiration of this Lease, for loss of use of the Main Building Area, or
for relocation  expenses;  provided,  however,  that Tenant's claims do not
reduce Landlord's award for its fee interest subject to Tenant's  leasehold
interest.  In such event, Tenant shall be entitled to receive such amounts.
Landlord  or any  Mortgagee  having a right  thereto  shall be  entitled to
receive any and all awards paid by the  condemning  authority in connection
with such partial Taking, provided that such condemnation award received by
Landlord or such Mortgagee,  less the reasonable costs incurred by Landlord
and such Mortgagee in connection with the collection of such award shall be
applied to the cost of such Restoration,  subject to the same conditions to
release set forth in Section 15 hereof.  Any balance of the award remaining
after completion of such Restoration and not used for such Restoration, may
be retained by Landlord or such Mortgagee.

                          (iii) Notwithstanding the foregoing provisions of
this Subsection (a), in the case of partial Taking of the Main Building, if
Landlord or Tenant shall reasonably determine that the remaining portion of
the  Main  Building  cannot  practicably  be  so  restored  to  a  complete
architectural unit or that such Restoration is not economically feasible or
that after the Restoration, the remainder of the Main Building would not be
suitable for the uses permitted  hereunder,  then either Landlord or Tenant
may  terminate  this  Lease by notice to the other  party,  and,  upon such
termination,   Tenant  and  Landlord  shall  have  no  further  obligations
hereunder,  except with respect to any  obligations  which arose or accrued
before the  termination of this Lease or to the extent  obligations  are to
survive the termination of this Lease as otherwise  provided in this Lease.
Any dispute as to the right of Landlord or Tenant to  terminate  this Lease
under  this  Subsection   (iii)  shall  be  determined  by  arbitration  in
accordance  with  Section  11(c).  In the  event of a Taking  that does not
result in the  termination  of this  Lease,  but results in a Taking of any
portion of the Main Building  Area,  Landlord  shall provide  Tenant with a
portion of the Unimproved Area for use for replacement  parking adjacent to
the  remaining  Main  Building  Area and access and  utilities  to the Main
Building  to the extent  such items are  affected  by the  Taking.  Nothing
herein shall be construed to require Landlord to incur any material expense
in connection therewith.

                  (b) In the event of a total  Taking of the Main  Building
Area,  this Lease  shall  terminate  as of the date title shall vest in the
condemnor  and,  upon such  termination,  Landlord and Tenant shall have no
further  obligations  hereunder,  except with respect to any breaches which
occurred before the termination of this Lease or to the extent  obligations
are to survive the termination of this Lease as otherwise provided in

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this Lease.  Landlord  shall be entitled to receive any and all awards paid
by the condemning  authority in connection with such Taking,  except to the
extent Tenant is entitled to recovery under Subsection 17(a)(ii).

                  SECTION 18.       LIENS

                  If,  because of any act or  omission  of Tenant or anyone
claiming by,  through,  or under Tenant,  any mechanic's lien or other lien
shall be filed against the Master Lease Property or any portion thereof, or
against  other  property of Landlord,  whether or not such lien is valid or
enforceable as such, Tenant shall, at its own expense, cause the same to be
discharged of record within a reasonable time, not to exceed 30 days, after
the date of filing  thereof,  and shall also defend and indemnify  Landlord
and any Mortgagee  and hold them harmless from any and all claims,  losses,
damages, judgments,  settlements,  costs and expenses, including reasonable
attorneys' fees,  resulting therefrom or incurred in connection  therewith.
Tenant shall not mortgage,  pledge,  hypothecate  or assign as security its
interest in the Master Lease Property or under this Lease.

                  SECTION 19.       EXISTING SPACE LEASES; ASSIGNMENT AND
                                            SUBLETTING

                  (a) On the Effective  Date,  the Main Building is subject
to those certain leases listed in Exhibit G attached hereto and made a part
hereof (the "Existing Space Leases"), which were entered into by Tenant, as
lessor thereunder, prior to closing under the Sales Agreement. Landlord has
not  assumed any of Tenant's  obligations  thereunder.  For so long as this
Lease  remains in  effect,  Tenant  covenants  and  agrees to  continue  to
discharge all of the lessor's  obligations under the Existing Space Leases,
whether  accrued  or  accruing  before or during  the  Term.  Tenant  shall
indemnify,  defend,  and hold harmless  Landlord  against any obligation of
Landlord  under the Existing  Space Leases  arising or accruing  during the
Term,  except to the extent Tenant is unable to perform such obligations as
a result of Landlord's breach of its obligations  under this Lease.  During
the Term, Tenant shall have the right to (i) collect and retain for its own
account  (subject to Subsection (c) below) all rents and other payments due
from tenants under Existing Space Leases  ("Existing  Tenants"),  (ii) hold
and apply any security  deposits of Existing Tenants in accordance with the
Existing Space Leases  (provided,  however,  that Tenant shall deliver such
security  deposits to Landlord at the expiration or earlier  termination of
this Lease to the extent such  security  deposits  have not been applied by
Tenant  pursuant to the applicable  Existing Space Lease or returned to the
applicable  Existing Tenant, and the term of the applicable  Existing Space
Lease extends beyond the Term),  and (iii)  terminate,  modify or otherwise
deal with the  Existing  Space  Leases as Tenant,  in its sole  discretion,
deems appropriate;  provided,  however,  (A) such right shall automatically
end upon the  termination  of this  Lease for any  reason,  (B) none of the
Existing Space Leases shall be modified to provide for a term

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which  extends  beyond the Term,  unless  Landlord  gives its prior written
consent to such extended term,  which consent may be granted or withheld in
Landlord's  sole  discretion,  (C) each  modification  of an Existing Space
Lease shall be subject and  subordinate to this Lease,  and in the event of
the expiration or termination of this Lease, Landlord shall not be required
to recognize such modification  without its express written agreement to be
bound by same, which may be given or not in Landlord's sole discretion, and
(D) Tenant  shall  promptly  provide to  Landlord  copies of all  documents
terminating or modifying any Existing Space Lease.

                  (b)  Tenant may  assign  its  interest  in this Lease (an
"Assignment")  or  sublet  all  or any  portion  of the  Main  Building  (a
"Sublease"), without the consent of Landlord. The term of any such Sublease
shall not exceed the Term,  unless Landlord gives its prior written consent
to such  extended  term,  which  consent  may be  granted  or  withheld  in
Landlord's  sole  discretion.  In the event of any  Assignment or Sublease,
Tenant shall  nevertheless at all times remain fully responsible and liable
for the  payment  of Rent  and the  performance  and  observance  of all of
Tenant's other obligations under this Lease. Each Sublease shall be subject
and subordinate to this Lease. If requested by Tenant, Landlord shall enter
into  a   nondisturbance   agreement   with  respect  to  any  Sublease  on
substantially  the  same  terms  as are  contained  in  the  nondisturbance
agreement  attached  hereto as Exhibit H (the  "Landlord  Approved  SNDA"),
provided  that (i) the Sublease does not, in any material  respect,  impose
greater  obligations  on the  sublandlord  or grant  greater  rights to the
subtenant  than those  existing as of the Effective Date under the Existing
Space  Leases,  (ii) term of the  Sublease  does not  extend  past the Term
(unless  expressly  approved by Landlord as provided above),  and (iii) the
Sublease (y) is an arms-length transaction and such subtenant was obtained,
and the economic  terms of such Sublease were  negotiated by, a third party
leasing  agent using  marketing  efforts  customarily  used for  Comparable
Properties,  or (z) requires the subtenant to pay basic rent at Fair Market
Sublease  Rent and a pro rata share of  increases  in  operating  expenses,
taxes and insurance (a "Non-Broker Sublease").  Landlord agrees at any time
hereafter, upon ten (10) business days prior written notice, to execute and
deliver, and cause its Mortgagee to recognize,  the Landlord Approved SNDA,
provided the Landlord  Approved  SNDA has been duly  executed by Tenant and
such  subtenant.  Promptly upon  entering into any  Assignment or Sublease,
Tenant shall provide  Landlord with copies of all documents  effecting such
Assignment or Sublease.

                  (c) In the event of a Non-Broker  Sublease,  Landlord and
Tenant shall attempt in good faith to agree as to the Fair Market  Sublease
Rent,  and if Landlord  and Tenant  fail to  promptly  agree as to the Fair
Market  Sublease Rent (the "Sublease  Arbitration  Deadline"),  Fair Market
Sublease Rent shall be determined as follows:

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                           (i)     Fair Market Sublease Rent shall be the rent
which would be asked of subtenants as of the anticipated  date of execution
of the Sublease for space  comparable  to the subject space of the Sublease
in the  Germantown/Clarksburg  areas of Montgomery County, Maryland, taking
into  account  the term of the  Sublease,  the size of the  premises  being
subleased and the value of brokerage commissions, rental abatements, rental
credits,  and tenant  allowances,  if any, being offered or paid under such
subleases.

                           (ii)  Landlord and Tenant shall use the same
methodology of the arbitration proceedings described in
Subsections 28(d)(ii) and (iii).

                  (d) As a part of  Additional  Rent,  Tenant  shall pay to
Landlord  one-half  of any Profit  derived  from any renewal of an Existing
Lease (a "Lease  Renewal") or from any  Assignment  or Sublease  during the
Term. As to each Lease Renewal,  Assignment,  and Sublease,  "Profit" shall
mean the excess,  if any, of the following:  the gross amount  collected by
Tenant under or with respect to the Lease Renewal,  Assignment, or Sublease
over a specific period of time (the "Measuring Period"),  less (i) the Base
Rent paid by Tenant to  Landlord  over the  Measuring  Period  for the same
space as is the subject of the Lease Renewal,  Assignment, or Sublease (the
"Subject Space"), (ii) all other amounts paid by Tenant with respect to the
Measuring  Period and relating to the Master Lease  Property as required by
this Lease,  pro-rated  based upon the rentable  area of the Subject  Space
compared to the rentable area of the Main Building,  (iii) a management fee
to Tenant  equal to three  percent  (3%) of the amount  collected by Tenant
under or with respect to the Lease  Renewal,  Assignment,  or Sublease over
the Measuring  Period,  (iv) all  reasonable  costs of  collection  paid by
Tenant to collect the sums payable under the Lease Renewal,  Assignment, or
Sublease,  and (v)  reasonable  and customary  brokerage  fees, the cost of
tenant improvements, reasonable attorneys' fees and all other out of pocket
costs paid by Tenant to third parties in connection with the Lease Renewal,
Assignment,  or Sublease. Tenant shall provide to Landlord on or before the
sixtieth  (60th) day following  each Lease Year in which Profit is received
by Tenant a calculation and payment of Profit for the preceding Lease Year.
The  calculation  shall  be  certified  by  Tenant  as being  accurate  and
complete,  to the best of its knowledge,  along with such  information  and
materials (including, but not limited to, copies of invoices,  calculations
and  allocations) in support thereof,  as Landlord may reasonably  request.
Despite  the  foregoing,  no  calculation  or  payment  of Profit  shall be
required  with respect to any  Assignment  or Sublease to a  subsidiary  of
Tenant or arising from a sale of any division or  subsidiary  of Tenant,  a
sale of all or substantially  all of the assets or capital stock of Tenant,
or any merger or consolidation of Tenant.

                  (e) If there is an Event of  Default,  in addition to any
other  remedies  provided  by this  Lease  or by law or in  equity,  at its
option, Landlord may collect directly from any Existing

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Tenant, Assignee or lessee under a Sublease ("Subtenant") all rent becoming
due to Tenant by reason of the  applicable  Existing  Lease,  Assignment or
Sublease. Any collection by Landlord from the Existing Tenant,  Assignee or
Subtenant  shall not be  construed  to  constitute a novation or release of
Tenant from the further  performance of its obligations under this Lease or
an acceptance of the terms of such Existing Lease, Assignment or Sublease.

                  (f) Any amounts collected by Landlord pursuant to Section
19(e) or otherwise from an Existing Tenant, Assignee or Subtenant which are
applicable to any period  preceding the Expiration Date (had this Lease run
its full Initial Term as may have been extended),  less Landlord's share of
any Profit  attributable  to such  amounts and less  Landlord's  reasonable
costs of  collection,  shall be applied by  Landlord  to the  reduction  of
Tenant's remaining liability, if any, under this Lease.

                  SECTION 20.       SUBORDINATION OR SUPERIORITY OF LEASE

                  (a) Except as  otherwise  provided in this  Section,  the
rights  and  interest  of Tenant  under this  Lease  shall be  subject  and
subordinate  to any  mortgages  that may be placed  upon the  Master  Lease
Property  and to any and all  advances  to be made  thereunder,  and to the
interest thereon, and all renewals, replacements,  extensions, bifurcations
and splits thereof,  if the Mortgagee named in said mortgage shall elect to
subject and  subordinate the rights and interest of Tenant under this Lease
to the lien of its mortgage. Any Mortgagee may elect to give the rights and
interest of Tenant under this Lease priority over the lien of its mortgage.
In the  event  of  either  such  election  and  upon  notification  by such
Mortgagee to Tenant to that effect, the rights and interest of Tenant under
this Lease shall be deemed to be subordinate  to, or to have priority over,
as the case may be, the lien of said mortgage,  whether this Lease is dated
prior to or  subsequent  to the date of said  mortgage  without any further
action  required by Landlord or  Mortgagee;  provided,  however,  that as a
condition  precedent to any subordination of this Lease,  Landlord delivers
in advance a  non-disturbance  agreement  duly  executed by  Mortgagee  and
Landlord. The non-disturbance  agreement shall be substantially in the form
attached  to and  made a part of  this  Lease  as  Exhibit  I (the  "Tenant
Approved  SNDA") or in a  commercially  reasonable  form and subject to the
approval of Tenant, not to be unreasonably  withheld.  Tenant agrees at any
time  hereafter,  upon ten (10)  business  days prior  written  notice,  to
execute and deliver the Tenant Approved SNDA.

                  (b)  Nothing  contained  in this  Lease  shall  limit  or
curtail  Landlord's right to sell,  mortgage or otherwise  transfer its fee
interest in the Master Lease Property, or affect Landlord's right to assign
the Rent payable  under this Lease either as  collateral  security  under a
mortgage or  otherwise.  Any such sale,  mortgage,  transfer or  assignment
shall be binding on Tenant but shall be subject to this Lease.



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                  SECTION 21.       DEFAULTS AND REMEDIES

                  (a) The  occurrence  of any one or more of the  following
events shall be a default and breach of this Lease by Tenant (collectively,
"Events of Default"):

                           (i)      Tenant shall fail to pay any installment of
Rent when the same shall be due and payable  and fail to cure such  default
within  nine  (9)  days  after  receiving   written  notice  from  Landlord
specifying  the default.  For the purposes of this  Subparagraph  21(a)(i),
Tenant  agrees notice by Mortgagee,  or Landlord's  loan service  provider,
given  according  to the terms of Section  26,  shall be deemed  sufficient
notice.

                           (ii)     Tenant shall fail to perform or observe any
other term,  condition,  covenant or obligation required to be performed or
observed  by it under  this  Lease for a period of thirty  (30) days  after
written notice from Landlord  specifying such default;  provided,  however,
that if the term,  condition,  covenant or  obligation  to be  performed by
Tenant is of such  nature  that the same  cannot  reasonably  be  performed
within such thirty (30) day period,  such  default  shall be deemed to have
been cured if Tenant commences such performance  within the thirty (30) day
period and thereafter diligently undertakes to complete the cure and in all
events cures the default within one hundred twenty (120) days of Landlord's
notice, subject to extension for Unavoidable Delays.

                           (iii) An Event of Default, as defined therein,
shall  occur  under  that  certain  lease  agreement,  dated  of even  date
herewith,  between  Landlord and Tenant with  respect to the  Installations
Premises (the "Facilities Lease").

                           (iv)  Termination or rejection of this Lease
pursuant to Section 22.

                           (v)   Assumption or assignment of this Lease, under
the  conditions  referred  to in Section  22,  unless the  requirements  of
Section 22 applicable to such assumption or assignment are satisfied.

                  (b) Upon the occurrence of any Event of Default, Landlord
shall have the following rights and remedies,  in addition to those allowed
by law or equity,  any one or more of which may be  exercised  concurrently
and without further notice to or demand upon Tenant:

                           (i)   Landlord may re-enter the Master Lease
Property  and cure any  default  of Tenant,  in which  event  Tenant  shall
reimburse Landlord as Additional Rent for any reasonable costs and expenses
which  Landlord may incur to cure such default;  and Landlord  shall not be
liable to Tenant for any loss or damage  which Tenant may sustain by reason
of Landlord's action, except loss or damage caused by Landlord's negligence
or intentional misconduct.

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                           (ii)   Landlord may terminate this Lease, in which
event:  (A) Tenant shall not  thereafter  be entitled to  possession of the
Master Lease Property and Tenant shall immediately thereafter surrender, or
cause to be  surrendered,  the  Master  Lease  Property  to  Landlord;  (B)
Landlord may re-enter the Master Lease  Property and  dispossess  Tenant by
summary  proceedings,  ejectment or other legal  process and may remove its
effects,  without prejudice to any other remedy which Landlord may have for
possession or  arrearages  in Rent;  and (C) Tenant shall be liable for all
loss or damage which Landlord may sustain by reason of such termination and
re-entry;  and  Landlord  may re-let  all or any part of the  Master  Lease
Property  for a  term  different  from  that  which  would  otherwise  have
constituted  the  balance  of the  Term  and  for  Rent  and on  terms  and
conditions different from those contained herein, whereupon Tenant shall be
obligated  to pay to  Landlord  the  deficiency,  if any,  between the Rent
provided  for  herein  and  that  provided  for in  any  lease  covering  a
subsequent  re-letting of the Master Lease  Property,  for the period which
would otherwise have constituted the balance of the Term, together with all
of Landlord's  reasonable  costs and expenses of preparing the Master Lease
Property for re-letting, including all repairs, tenant finish improvements,
brokers' and  attorneys'  fees,  and all loss or damage which  Landlord may
sustain by reason of such  re-letting,  it being  expressly  understood and
agreed that the liabilities and remedies  specified above shall survive the
termination of this Lease. Landlord shall make diligent efforts to mitigate
its damages in the event of an Event of Default.

                           (iii) (A) Notwithstanding the termination of this
Lease,  Landlord  may declare all Base Rent which would have been due under
this Lease for the balance of the Term to be immedi  ately due and payable.
In that  event,  Tenant  shall be  obligated  to pay an amount in cash that
would be necessary to purchase U.S.  Obligations in such amounts and having
such  maturities  that the principal and interest of such U.S.  Obligations
would be  sufficient  to provide funds as close as possible but in no event
less or later  than the  payments  due under this Lease as Base Rent as and
when such  payments  would be due if no  acceleration  of the Base Rent had
occurred (the "Accelerated  Payment").  U.S. Obligations are obligations or
securities not subject to prepayment,  call or early  redemption  which are
direct obligations of, or obligations fully guaranteed as to timely payment
by, the United States of America or any agency or instrumentality  thereof,
the  obligations  of which are  backed by the full  faith and credit of the
United States of America.

                           (B) Upon receipt of the Accelerated Payment,
Landlord  shall use  commercially  reasonable  efforts  to lease the vacant
areas of the Main  Building  at the then  currently  existing  fair  market
rental rate for Comparable  Buildings.  From and after the Event of Default
all rent and other payments, except for security deposits,  collected under
leases entered into after the Event of Default ("Post Default  Leases") and
under any Existing  Space  Leases,  Subleases,  or occupancy or  concession
agreements  in  effect  as of the  Event of  Default  shall be  placed in a
separate

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escrow  account  (the  "Escrow  Account")  held  by a  mutually  acceptable
escrowee (the "Escrowee").  Also, any refunds of Impositions paid by Tenant
and received by Landlord shall be placed in the Escrow Account.  The Escrow
Account shall be interest  bearing and earn at least a money market rate of
interest.  All interest  earned shall become part of the escrow fund and be
treated in the same manner as the principal in the Escrow Account. The Post
Default Leases and all Existing Space Leases,  Subleases, and occupancy and
concession agreements in effect as of the Event of Default are collectively
referred to as the "Mitigation  Leases".  The funds contained in the Escrow
Account shall be disbursed in the  following  manner and with the following
priority:  (i) all direct and  reasonable  operating  expenses  ("Operating
Expenses")  paid by Landlord  relating to the Master Lease Property  during
the "Default  Measuring  Period" (defined below) shall be paid to Landlord,
(ii) a management  fee equal to three percent (3%) of the amount  collected
by Landlord from the Mitigation  Leases during the Default Measuring Period
shall  be paid to  Landlord,  (iii)  all  direct  and  reasonable  costs of
collection  paid  by  Landlord  to  collect  the  sums  payable  under  the
Mitigation Leases shall be paid to Landlord,  (iv) reasonable and customary
brokerage  fees,  the  reasonable  cost  of  designing,   constructing  and
installing tenant  improvements,  reasonable  attorneys' fees and all other
reasonable  out of  pocket  costs  paid  by  Landlord  during  the  Default
Measuring Period to third parties in connection with the Mitigation  Leases
(including  the fees of the Escrowee and the Escrow  Account) shall be paid
to  Landlord,  (v) Tenant  shall be paid up to the amount  that  Tenant was
scheduled to pay as Base Rent during the Default Measuring Period, and (vi)
the remainder  shall be shared  equally by Landlord and Tenant.  As used in
this Section,  the term "Default Measuring Period" shall mean (1) as to the
payments  contemplated in (i) through (iv) above,  each consecutive one (1)
month period after the  establishment  of the Escrow Account until the date
the Term would have  expired but for the early  termination  of this Lease,
and  (2) as to the  payments  contemplated  in (v)  and  (vi)  above,  each
consecutive  three (3) month period after the  establishment  of the Escrow
Account  until  the date the Term  would  have  expired  but for the  early
termination of this Lease.  The first Default  Measuring  Period,  however,
shall also  include the period from the date of the Event of Default to the
date the Escrow Account was established.  Escrowee shall make disbursements
to the parties in the priority  described  above on or about the  fifteenth
(15th) day after the end of each Default Measuring Period.  Within ten (10)
days  after  the end of  each  Default  Measuring  Period  relating  to the
payments  contemplated in (i) through (iv) above, Landlord shall furnish to
Escrowee and Tenant a written  statement setting forth in reasonable detail
all amounts paid into the Escrow Account and all amounts for which Landlord
is claiming  payment  with  respect to the  immediately  preceding  Default
Measuring  Period.  The  statement  shall be certified by Landlord as being
accurate  and shall be  accompanied  by  invoices  and other  documentation
reasonably  evidencing  the amounts  claimed for  payment.  Escrowee  shall
withhold from the payments made under (v) and (vi) above one-fourth of the

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<PAGE>
 
reasonably  estimated  real estate taxes and Insurance  premiums  which are
next due with respect to the Master Lease Property, less the amounts of any
real estate taxes or  Insurance  premiums  required to be directly  paid by
tenants under the  Mitigation  Leases (the "Tax and Insurance  Holdbacks").
Escrowee shall release Tax and Insurance  Holdbacks to Landlord when and to
the extent that real estate  taxes and  Insurance  premiums  are payable by
Landlord  with  respect to the Master Lease  Property.  At the time of each
such  disbursement to Landlord,  Escrowee shall also disburse to Tenant the
amount,  if any, by which the Tax and Insurance  Holdbacks held by Escrowee
exceed the tax bill or Insurance  premiums paid with such Tax and Insurance
Holdbacks. Although the last Default Measuring Period shall end on the date
the Term would have  expired but for the early  termination  of this Lease,
any amounts  collected by Landlord under the  Mitigation  Leases after that
date and attributable to any period which occurred prior to that date shall
be paid  directly  by  Landlord  to Tenant.  No party shall be paid for any
amount  described  in this  Subsection  (B) to the  extent  such  party was
otherwise  reimbursed  for  such  amount,  including,  without  limitation,
previous  payment  by the  Escrowee  or  previous  reimbursement  under the
Mitigation Leases. For the purposes of this Section,  "Operating  Expenses"
includes the amortized cost of capital  improvements  properly allocable to
the Default  Measuring Period but excludes (1) debt service and other costs
of Landlord's financing, (2) capital expenditures (except for the amortized
portion properly allocable to the Default Measuring Period), (3) management
fees, (4) overhead, (5) depreciation, (6) accountants' fees, (7) any losses
or expenses covered by Insurance,  whether or not such Insurance is in fact
maintained,  or  compensable  by  condemnation  proceeds,  (8)  any  amount
incurred by reason of the negligence or intentional  misconduct of Landlord
or its  Agents,  (9)  fines or  penalties,  and (10)  any  amounts  paid by
specific  tenants.  Any refunds,  discounts,  or  recoupments  of Operating
Expenses  received  by Landlord  shall be  accounted  for by  Landlord  and
credited back to Tenant.  Tenant,  at reasonable  times and upon reasonable
notice, shall have the right to audit Landlord's books and records relating
to Operating  Expenses;  provided,  however,  in no event shall Landlord be
required to keep such underlying  receipts for Operating  Expenses beyond a
date which is three (3) years after Escrowee makes a disbursement  for such
Operating  Expenses.  The cost of capital  expenditures  shall be amortized
over the useful life of each such capital  expenditure  as  determined  for
federal income tax purposes.  Notwithstanding the foregoing, Landlord shall
not be entitled to payment from the Escrow Account for any costs of capital
improvements,  repairs,  or  maintenance  that  Tenant  would not have been
obligated to  undertake  under the standard of Care set forth in Section 11
of this Lease or for any other  Operating Costs which Tenant would not have
been  obligated  to pay under this Lease.  Notwithstanding  anything to the
contrary contained herein, until the expiration of 91 days after Landlord's
receipt of the Accelerated Payment, Tenant shall not make any claim against
Landlord that  Landlord has failed to use diligent  efforts to mitigate its
damages after the Event of

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Default which gave rise to the  Accelerated  Payment.  This provision shall
survive the termination of this Lease.

                           (C) In the event that Landlord exercises its
remedy under Subsection (iii)(A) of this Section, performance of Landlord's
obligations  under  Subsection  (iii)(B) of this Subsection shall be deemed
satisfaction of Landlord's duty to mitigate its damages.

                           (iv)   Landlord may sue for injunctive relief or to
recover damages for any loss resulting from the breach.

                  (c) Any agreement for an extension of the Term or for any
other  additional  period after the Term shall not thereby prevent Landlord
from  terminating this Lease for any reason specified in this Lease. If any
such right of termination  is exercised by Landlord  during the Term or any
extension  thereof,  Tenant's  right to any extension or additional  period
shall thereby be automatically  canceled.  Any such right of termination of
Landlord contained herein shall continue during the Term and any subsequent
extension hereof.

                  (d) The  failure  or delay by either  party to enforce or
exercise at any time any of the rights or remedies or other  provisions  of
this Lease shall not be  construed to be a waiver  thereof,  nor affect the
validity of any part of this Lease or the right of that party thereafter to
enforce each and every such right or remedy or other provisions.  No waiver
of any  default or breach of this Lease shall be held to be a waiver of any
other  default or breach.  No act or omission  by Landlord  during the Term
shall be deemed an acceptance  of a surrender of the Master Lease  Property
and no  agreement  to  accept  such a  surrender  shall be valid  unless in
writing and signed by Landlord.

                  (e) If either  party  defaults  under  this Lease and the
other party places the  enforcement of all or any part of this Lease or the
collection of any sum due or to become due under this Lease or the recovery
of possession of the Master Lease Property in the hands of an attorney, and
such party  prevails in litigation  concerning  such issue,  the defaulting
party  agrees  to  reimburse  the  prevailing   party  for  the  reasonable
attorney's fees incurred thereby.

                  SECTION 22.       BANKRUPTCY OR INSOLVENCY

                  Landlord and Tenant agree that the following  shall apply
in the event of the bankruptcy or insolvency of Tenant:

                  (a) If a petition  is filed by, or an order for relief is
entered  against  Tenant  under  Chapter 7 of the  Bankruptcy  Code and the
trustee of Tenant  elects to assume this Lease for the purpose of assigning
it, such assumption and assignment may be made only if all of the terms and
conditions of Subsections (b) and (d) below are satisfied. To be effective,
an election to assume this Lease must be in writing, addressed to Landlord, and

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all of the conditions herein stated,  which Landlord and Tenant acknowledge
to be commercially  reasonable,  must have been  satisfied.  If the trustee
fails so to elect to assume  this Lease  within  sixty (60) days after such
filing or order or such additional time as the Bankruptcy Court, for cause,
may fix,  this Lease  will be deemed to have been  rejected,  and  Landlord
shall then  immediately  be  entitled  to  possession  of the Master  Lease
Property  without  further  obligation  to Tenant or the trustee,  and this
Lease shall be terminated.  Landlord's  right to be compensated for damages
in the bankruptcy proceeding, however, shall survive such termination.

                  (b) If Tenant files a petition for  reorganization  under
Chapters 11 or 13 of the  Bankruptcy  Code, or if a pro ceeding filed by or
against Tenant under any other chapter of the Bankruptcy  Code is converted
to a  chapter  11 or 13  proceeding  and  Tenant's  trustee  or  Tenant  as
debtor-in-possession  fails to assume  this  Lease  within 60 days from the
date of the filing of such petition or conversion or such  additional  time
as the  Bankruptcy  Court,  for  cause,  may fix,  then the  trustee or the
debtor-in-possession  shall be deemed to have  rejected  this Lease.  To be
effective, any election to assume this Lease must be in writing,  addressed
to Landlord  and, if there has been a default  under the Lease,  all of the
following   conditions,   which  Landlord  and  Tenant  acknowledge  to  be
commercially reasonable, must have been satisfied:

                           (i)      The trustee or the debtor-in-possession has
                                    cured or has provided to Landlord adequate
                                    assurance that:

                                    (A)     It  will   cure  all   monetary
                                            defaults   under   this   Lease
                                            within   the   number  of  days
                                            specified  in Section  21(a)(I)
                                            of this  Lease from the date of
                                            assumption; and

                                    (B)     It will  cure  all  nonmonetary
                                            defaults   under   this   Lease
                                            within   the   number  of  days
                                            specified in Section  21(a)(ii)
                                            of this  Lease from the date of
                                            assumption.

                           (ii)     The trustee or the debtor-in-possession
                                    has   compensated   Landlord,   or  has
                                    provided    Landlord    with   adequate
                                    assurance   that   Landlord   will   be
                                    compensated  promptly for any pecuniary
                                    loss it has  incurred  arising from the
                                    default of Tenant, the trustee,  or the
                                    debtor-in-possession.

                           (iii)    The trustee or the debtor-in-possession
                                    has  provided  Landlord  with  adequate
                                    assurance of the future  performance of
                                    each of Tenant's obligations under this
                                    Lease; provided,
                                    however, that:


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<PAGE>
 
                                    (A)     From  and  after  the  date  of
                                            assumption of this Lease, until
                                            the date of the  assignment  of
                                            this  Lease,  it shall  pay all
                                            monetary           obligations,
                                            including,  without limitation,
                                            the  Rent  payable  under  this
                                            Lease,  in advance on each date
                                            that such amounts are payable.

                                    (B)     It  shall  also   deposit  with
                                            Landlord,  as security  for the
                                            timely   payment  of  Rent,  an
                                            amount  equal to three  months'
                                            Base  Rent and  other  monetary
                                            charges   accruing  under  this
                                            Lease;

                                    (C)     If not  otherwise  required  by
                                            the  terms  of this  Lease,  it
                                            shall also pay in  advance,  on
                                            each day  that any  installment
                                            of  Base   Rent   is   payable,
                                            one-twelfth  (1/12) of Tenant's
                                            Imposition, Insurance and other
                                            obligations under this Lease.

                  (c)  If  the  trustee  or  the  debtor-in-possession  has
assumed this Lease,  pursuant to Subsection (a) or (b) above, and elects to
assign  Tenant's  interest  under this Lease or the estate  created by that
interest to any other person,  such interest or estate may be assigned only
if  the  intended  assignee  has  provided  adequate  assurance  of  future
performance of all of the terms, covenants, and conditions of this Lease.

For the  purposes of this  Subsection  (d),  "adequate  assurance of future
performance" means that Landlord has ascertained that each of the following
condition has been satisfied:

                           The  assignee  has  submitted a current
                           financial  statement which shows a net worth and
                           working capital in amounts  sufficient to assure
                           the  future   performance  by  the  assignee  of
                           Tenant's obliga tions under this Lease.

                  (d)  When, pursuant to the Bankruptcy Code, the trustee or
the  debtor-in-possession  is obligated to pay reasonable use and occupancy
charges  for the use of all or part of the  Master  Lease  Property,  it is
agreed that such  charges will not be less than the Base Rent as defined in
this Lease,  plus Additional Rent and other monetary  obligations of Tenant
included herein.

                  (e)  Except  to  the  extent  provided  by  law,  neither
Tenant's  interest  in this Lease nor any estate of Tenant  created in this
Lease  shall pass to any  trustee,  receiver,  assignee  for the benefit of
creditors, or any other person or entity, nor otherwise by operation of law
under the laws of any state having  jurisdiction  of the person or property
of Tenant, unless Landlord consents in writing to such transfer. Landlord's
acceptance  of Rent or any  other  payments  from  any  trustee,  receiver,

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assignee, person, or other entity will not be deemed to have waived, or waive,
either the requirement of Landlord's consent or Landlord's right to terminate
this Lease for any transfer of Tenant's  inter est under this Lease without
such consent.

                  SECTION 23.       SURRENDER OF MASTER LEASE PROPERTY

                  Upon the expiration or earlier termination of this Lease,
Tenant shall surrender the Master Lease Property to Landlord,  broom-clean,
in good order,  condition and repair (except for ordinary wear and tear and
conditions  which  existed  on  the  Master  Lease  Property  prior  to the
Effective  Date and subject to Sections  15 and 17),  free of all  Personal
Property and Restricted  Property (except for Restricted Property belonging
to any  Existing  Tenant or  Subtenant  whose  Existing  Lease or  Sublease
Landlord  has  expressly  agreed  in  writing  may  continue),  and free of
violation of Applicable  Laws in all material  respects  subject to Section
5(b)(iv).  To the extent  Tenant fails to comply with the  requirements  of
this  Section,  Landlord  may  restore  the Master  Lease  Property to such
condition at Tenant's expense.

                  SECTION 24.       NON-CONSENSUAL HOLDING OVER

                  In the event Tenant  remains in  possession of the Master
Lease  Property or any part thereof  without the consent of Landlord  after
the  expiration  or earlier  termination  of this  Lease,  Tenant  shall be
deemed,  at  Landlord's  election,  to hold the Master Lease  Property as a
tenant at sufferance subject to all of the terms, conditions, covenants and
provisions  of this Lease which shall be  applicable  during such time (the
"Non- Consensual Holdover Period"),  except that, for each month during the
Non-Consensual  Holdover  Period,  Tenant shall pay to Landlord one hundred
fifty  percent  (150%)  of  the  sum  of  the  last  current  full  monthly
installment of Base Rent plus  Additional  Rent,  which shall be payable to
Landlord  within  five  (5)  business  days of  notice  from  Landlord.  In
addition, such election shall not preclude Landlord from seeking, and shall
be cumulative  with, any other remedy under this Lease or granted by law or
in equity.  No holding  over by Tenant,  as  described  in this Section 24,
whether  with or without the consent of Landlord,  shall  operate to extend
this Lease.

                  SECTION 25.       QUIET ENJOYMENT

                  If and for so long as Tenant pays the prescribed Rent and
performs  or  observes  all  of  the  terms,   conditions,   covenants  and
obligations  of this Lease  required  to be  performed  or  observed  by it
hereunder, Tenant shall at all times during the Term have the peaceable and
quiet enjoyment, possession, occupancy and use of the Master Lease Property
without any inter  ference from  Landlord,  or anyone  claiming  through or
under  Landlord,  subject to any matters of record as of the Effective Date
to which this Lease is subject.

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                  SECTION 26.       NOTICES

                  Any notice, demand or request required or permitted to be
given  under  this Lease or by law shall be deemed to have been given if in
writing and delivered addressed to the party who is to receive such notice,
demand or request at the address  set forth below or at such other  address
as  Landlord or Tenant may  specify  from time to time by notice.  Delivery
hereunder  shall be deemed  to  include  pre-paid  courier  delivery  (by a
reputable  courier delivery  service),  pre-paid  overnight  delivery (by a
reputable  overnight delivery  service),  postage and fees paid U.S. Postal
Service  express mail or  certified  mail,  return  receipt  requested,  or
facsimile transmission with electronic  verification during normal business
hours,  if sent to the address of the  parties  designated  hereunder,  and
shall be deemed  received on the next business day such notice is delivered
or  refused  at such  address  except  notices  sent by fax shall be deemed
received upon electronic verification.

         Landlord:        LCOR Incorporated
                          6701 Democracy Boulevard
                          Bethesda, MD  20817
                          Attn: Mr. R. William Hard
                          Facsimile: (301) 897-3713

         with copies to:  Jones, Day, Reavis & Pogue
                          1450 G Street, N.W.
                          Washington, DC 20005-2088
                          Attn: Sigmund T. Weiner, Esq.
                          Facsimile: (202) 737-2832

                          LCOR Incorporated
                          300 Berwyn Park, Suite 104
                          Berwyn, PA 19312
                          Attention: Mr. Peter DiLullo
                          Facsimile: (610) 408-4420

         Tenant:          COMSAT Corporation
                          6560 Rock Spring Drive
                          Bethesda, MD 20817
                          Attention: General Manager Corporate
                                     Services
                          Facsimile: (301) 214-7147

         with a copy to:  COMSAT Corporation
                          6560 Rock Spring Drive
                          Bethesda, MD 20817
                          Attention: General Counsel

                          Facsimile: (301) 214-7128

Any copies required to be sent as above provided are for the convenience of
the  parties  and no such copy  shall  constitute  adequate  notice for the
purposes of this Section.

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                  SECTION 27.       HAZARDOUS MATERIALS

                  Landlord  and Tenant agree as follows with respect to the
existence or use of "Hazardous Material" on the Master Lease Property or in
the Main Building.

                  (a)  If  the  use,  storage,  handling,   generation,  or
disposal of Hazardous  Material on or in the Master Lease  Property  during
the  Term  results  in the  release  or  threatened  release  of  Hazardous
Materials  at,  on or under the  Master  Lease  Property  in  violation  of
Applicable  Law,  or  otherwise  necessitates  investigation  or cleanup of
Hazardous  Material  as  required  under  Applicable  Law   ("Environmental
Conditions"),  Tenant shall  indemnify,  defend and hold Landlord  harmless
from any and all  claims,  judgments,  damages,  penalties,  fines,  costs,
liabilities  or  losses  (including,   without  limitation,  sums  paid  in
settlement of claims,  attorneys' fees, consultant fees and expert fees but
excluding  consequential  damages  and  any  injury  to  the  value  of the
Property,  provided that this clause shall not be construed as reducing the
Remediation  Obligation)  which arise  during or after the Term as a direct
result  thereof.  This  indemnification  of  Landlord  by Tenant  includes,
without  limitation,  reasonable  costs  incurred  in  connection  with any
investigation  of site  conditions  or any  cleanup,  remedial,  removal or
restoration  work  required  by any  federal,  state or local  governmental
agency because of Hazardous  Material present in the soil or groundwater on
or under the Master  Lease  Property or in any  improvements  on the Master
Lease  Property.  This  indemnification,  however,  shall  not apply to any
Environmental Conditions caused by the acts or omissions of Landlord or its
Agents. The indemnification  and hold harmless  obligations of Tenant under
this Section 27 shall survive any termination of this Lease for a period of
twenty-four  (24)  months  after  the  termination.   At  the  end  of  the
twenty-four  (24) month period,  this  indemnification  and all of Tenant's
obligations  under  this  Section  shall  expire,   except  as  to  matters
specifically  made the subject of a lawsuit filed against Tenant before the
expiration  of the  twenty-four  (24) month  period.  Without  limiting the
foregoing,  if the use,  storage,  handling,  generation,  or  disposal  of
Hazardous  Material  on or in the  Master  Lease  Property  during the Term
results  in  any  Environmental   Conditions,   then,   provided  that  the
Environmental  Condition is not caused by the acts or omissions of Landlord
or its Agents, Tenant shall promptly take all actions, at its sole expense,
as are necessary to return the Master Lease Property to  substantially  the
condition  existing  prior to  thereto or to such  other  condition  as may
satisfy  the  applicable   governmental   authorities   (the   "Remediation
Obligation").  Landlord's approval of such actions shall first be obtained,
which approval shall not be unreasonably withheld.  Nothing in this Section
shall be deemed to prohibit or limit any action by Tenant against any party
or parties responsible for the contamination.

                  (b)  Landlord  and  Tenant   acknowledge   that  asbestos
containing  materials  ("ACM") are located in certain  portions of the Main
Building. Except for the ACM to be removed by Tenant as part of the Roof Work,
and so long as not required by Applicable Laws, Tenant shall not be required to

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remove or otherwise treat or abate the other ACM located in the Main Building;
provided, that during the Term Tenant covenants and agrees (i) to continue
implementation of the Operations and Maintenance  Plan described in Exhibit J 
attached hereto and made a part hereof at all times in compliance  with 
Applicable Laws in all material respects; (ii) to take such actions with 
respect to the ACM as may be  necessary to comply with Applicable Laws  and to
maintain the habitability of the Main Building; and (iii) to indemnify and hold
Landlord harmless (except to the extent caused by Landlord) from any and all
claims, judgments,   damages,   penalties,  fines,  costs,  liabilities  or
losses (including,  without limitation, reasonable attorneys' fees and  costs)
arising out of or relating to claims for tort  liability  brought by Tenant
or its Agents for events  occurring or accruing during the Term as a result
of the existence of the ACM in the Main Building.

                  (c) Landlord shall have the right,  at any time, to cause
the groundwater, soil, improvements and air at the Master Lease Property to
be  investigated  to detect the presence of Hazardous  Material  during the
Term, including,  but not limited to, the installation of testing wells and
other  devices  in  locations  selected  by  Landlord  at  Landlord's  sole
discretion. Landlord shall supply Tenant with copies of final investigation
reports. The cost of such investigations and of the maintenance, repair and
replacement  of such  wells and other  devices  shall be fully  paid for by
Landlord,  unless Landlord's investigations reveal Environmental Conditions
which Tenant is obligated to remediate  under this Section.  In that event,
Tenant,  within 30 days after receiving a copy of such investigation report
and a statement  of charges  from  Landlord,  shall pay for the cost of the
investigation.  Any dispute under this  Subsection  shall be resolved under
the arbitration proceedings set forth in Subsection 11(c).

                  (d) As used herein,  the term "Hazardous  Material" means
any  hazardous  or toxic  substance,  material or waste which is or becomes
regulated by any local governmental authority, the State of Maryland or the
United  States  Government  or other  Applicable  Law. The term  "Hazardous
Material" includes,  without limitation, any material or substance which is
(i)  designated as a "hazardous  substance"  pursuant to Section 307 of the
Federal  Water  Pollution  Control Act, 33 U.S.C.  Section 1251 et seq. (33
U.S.C.  Section  1317),  (ii)  defined as a "hazardous  waste"  pursuant to
Section 3001 of the Federal  Solid Waste  Disposal  Act, 42 U.S.C.  Section
6901 et seq. (42 U.S.C.  Section  6921),  or (iii)  defined as a "hazardous
substance"  pursuant  to  Section  101 of the  Comprehensive  Environmental
Response,  Compensation  and Liability Act, 42 U.S.C.  Section 9601 et seq.
(42  U.S.C.   Section  9601),   or  (iv)  petroleum,   petroleum   product,
polychlorinated biphenyls or urea formaldehyde.

                  (e) Within 30 days of the  Expiration  Date, if requested
by Landlord, Tenant shall remove all fuel oil and other liquid contents and
Hazardous  Materials  (collectively,   the  "Contents")  from  all  now  or
hereafter active underground storage tanks located on the Master Lease Property

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and dispose of such contents off of the Master Lease Property and in accordance
with Applicable Laws. Tenant shall  not be  obligated  to  remove,  close or
take any  other  action  to de-commission  the tanks during or after the Term.
If, however,  during the Term governmental authorities require such removal,
closure or other action and the  requirement  is not prompted by  Landlord's
request to remove the Contents or any Development by Landlord or its Agents,
Tenant shall comply with such request subject to Subsection 5(B)(iv)(d).

                  (f)  Notwithstanding  anything  contained  in this Lease,
Tenant shall have no obligation or liability to Landlord with respect to:

                           (i)      Any Hazardous Material which may exist on 
the Master Lease Property as of the Effective  Date,  except to the extent that
Tenant is  specifically  required to take action  regarding  such Hazardous
Material by the governmental authority having jurisdiction.

                           (ii)     Hazardous Material that migrates, flows,
percolates,  diffuses  or in any way moves on to or under the Master  Lease
Property from sources outside the Master Lease Property.

                           (iii) Hazardous Material present on or in the
Master  Lease  Property as a result of any  discharge,  dumping or spilling
(whether  accidental or  otherwise) on areas of the Master Lease  Property,
except the Main Building Area, by persons other than Tenant or its Agents.

                  SECTION 28.       RIGHT TO RENEW TERM

                  (a)  Provided  that this  Lease is then in full force and
effect,  and  provided  that no Event of Default  exists at the time of the
Renewal Notice or the date of  commencement  of the Renewal Term,  Landlord
hereby grants to the Tenant an option (the  "Renewal  Option") to renew the
Initial Term of this Lease on the same terms,  conditions and provisions as
contained in this Lease,  except as noted herein,  for a period of five (5)
years after the Expiration  Date of the Initial Term (the "Renewal  Term"),
which  Renewal  Option  period shall,  except as provided  below,  commence
immediately  following the  expiration of the Initial Term and end at 11:59
p.m. of the fifth anniversary of such date.

                  (b) The Renewal Option shall be exercised,  if at all, by
written  notice  (the  "Renewal  Notice")  from  Tenant to  Landlord of its
election, said notice to be given no later than the twenty-four (24) months
prior to the Expiration  Date of the Initial Term. If the Renewal Notice is
not so given by Tenant to  Landlord,  the  Renewal  Option  shall be deemed
waived.

                  (c) The  Renewal  Term  shall  be upon  the  same  terms,
covenants and conditions as provided in this Lease except as follows:

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                           (i)  Tenant shall not have any further right to
extend the Term or holdover after the end of the Term.

                           (ii) The annual Base Rent for the first year of
the Renewal  Term shall be equal to the lesser of (i) the Fair Market Rent,
and (ii) one hundred two and 75/100ths  percent  (102.75%) of the Base Rent
rate in effect under this Lease  immediately  prior to  commencement of the
Renewal Term; but in no event less than the annual Base Rent rate in effect
during the sixth Lease Year of the Initial Term (as reflected in Subsection
4(a)(vi)).

                           (iii) The annual Base Rent shall be increased
during the Renewal Term by two and 75/100ths  percent (2.75%) per year on a
cumulative compounded basis.

                  (d) Landlord  and Tenant  shall  attempt in good faith to
agree as to the Fair Market Rent,  and if Landlord and Tenant fail to agree
as to the Fair Market Rent at least six (6) months prior to the  Expiration
Date of the Initial  Term (the  "Arbitration  Deadline"),  Fair Market Rent
shall be determined as follows:

                           (i)   Fair Market Rent shall be the triple net rent
which  would be  asked of  tenants  as of the date of  commencement  of the
Renewal Term for space  comparable to the Main Building under five (5) year
leases in the  Germantown/Clarksburg  areas of Montgomery County, Maryland,
taking into account the size of the premises being leased by Tenant and the
value of brokerage  commissions,  rental  abatements,  rental credits,  and
tenant allowances, if any, being offered or paid under such leases.

                           (ii)   Tenant shall initiate the process to
determine  Fair Market Rent by giving  written  notice to Landlord  setting
forth  the name and  address  of a  leasing  broker  selected  by Tenant to
determine  the Fair  Market  Rent.  Within  five (5) days after  receipt of
Tenant's  notice,  Landlord  shall notify Tenant in writing of the name and
address of a leasing  broker  selected by Landlord  to  determine  the Fair
Market Rent. Each broker shall  independently make his or her determination
of the Fair Market Rent within  twenty (20) days after the  appointment  of
Landlord's  broker.  The Fair Market Rent shall be deemed to be the average
of the two  determinations  unless  the  higher of such  determinations  is
greater  than  one  hundred  five  percent  (105%)  of  the  lower  of  the
determinations.  If the higher  determination  is greater  than one hundred
five (105%) of the lower  determination,  the brokers  selected by Landlord
and Tenant shall together  select a third broker within five (5) days after
rendering their  determinations.  The third broker shall have ten (10) days
to make his or her  determination  of the Fair  Market  Rent and upon  such
determination,  the Fair  Market  Rent  shall be  deemed  to be the  median
determination  made by the three (3)  brokers.  If  Landlord  fails to give
Tenant  timely  notice of  Landlord's  selection  of a broker,  the  broker
selected by Tenant shall solely determine Fair Market Rent.

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                          (iii) Each broker appointed pursuant to this
Subsection  shall  be a  disinterested  broker  licensed  in the  State  of
Maryland having  recognized  competence in the field of commercial  leasing
and a minimum of ten (10) years  experience as a commercial  leasing broker
or agent in the Montgomery  County area.  Each party shall pay for the cost
of the broker which it selects and the parties shall share equally the cost
of the third broker, if any.

                  (e) Upon the valid  exercise  by  Tenant  of the  Renewal
Option,  at the request of either party hereto and within  thirty (30) days
after  such  request,  Landlord  and  Tenant  shall  enter  into a  written
supplement to this Lease incorporating the terms, conditions and provisions
applicable  to the  Renewal  Term as  determined  in  accordance  with  the
provisions of this Section;  provided,  that if the amount of Base Rent for
the first year of the Renewal Term has not then been set, such amount shall
be entered into such supplement when determined.

                  SECTION 29.       SECURITY DEPOSIT

                  If at any time  during  the Term,  the  credit  rating of
Tenant's  corporate  debt drops below BBB as rated by Standard & Poor's (or
the  equivalent  rating by any other national  rating agency  designated by
Landlord),  upon  notice from  Landlord,  Tenant  shall  deposit a sum with
Landlord  equal to one month's  installment of the then  applicable  annual
Base Rent  ("Security  Deposit"),  as  security  for the full and  faithful
performance by Tenant, of each and every term,  covenant,  and condition of
this Lease.  If there an event of Default,  Landlord  may use the  Security
Deposit as payment of any Rent or other payment due from Tenant to Landlord
or to otherwise  cure any default of Tenant  hereunder.  To the extent that
any of the Security Deposit is used for this purpose, Tenant shall pay such
amount to Landlord  along with the next  month's Rent in order to replenish
the Security  Deposit to the original  amount stated  herein.  The Security
Deposit  shall  be  returned  to  Tenant  within  thirty  (30)  days of the
Expiration  Date or earlier  termination  of this Lease to the extent  that
such  amount is not  depleted  in order to  remedy  any  default  by Tenant
hereunder.

                  SECTION 30.       MISCELLANEOUS GENERAL PROVISIONS

                  (a) Payments Deemed Rent. Any amounts of money to be paid
by Tenant to Landlord pursuant to the provisions of this Lease,  whether or
not such payments are  denominated  Rent or Additional  Rent and whether or
not  they  are to be  periodic  or  recurring,  shall  be  deemed  Rent  or
Additional  Rent for purposes of this Lease;  and any failure to pay any of
same shall  entitle  Landlord  to exercise  all of the rights and  remedies
afforded  hereby or by law or in equity for the collection and  enforcement
of Tenant's  obligation  to pay Rent.  Tenant's  obligation to pay any such
Rent or  Additional  Rent  pursuant to the  provisions  of this Lease shall
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this Lease and the surrender of possession of the Master Lease Property.

                  (b)  Interest  on  Deposits.  Any amount  deposited  with
Landlord under this Lease shall be held by Landlord in a federally insured,
interest bearing account.  Any interest earned on such deposit shall accrue
to Tenant and shall be transferred to Tenant  promptly after the Expiration
Date or such earlier time as may be specified in this Lease unless Landlord
is required by  Applicable  Laws to return such  interest to Tenant  sooner
than stated  herein.  Any amount  deposited with Mortgagee by Tenant (or by
Landlord  on  Tenant's  behalf)  shall  be held by  Mortgagee  pursuant  to
Applicable Laws and pursuant to the security documents between Landlord and
Mortgagee.  No interest shall accrue unless  required by Applicable Laws or
such security documents.  Notwithstanding the foregoing, any amounts placed
in the Escrow  Account  shall be governed by the  provisions  of Subsection
21(b)(iii)(B).

                  (c)      Landlord Cross Default.  Any default by Landlord
under the Facilities Lease shall be a default by Landlord under
this Lease.

                  (d)  Estoppel  Letters.  Tenant  shall,  within  ten (10)
business days following written request from Landlord, execute, acknowledge
and  deliver to Landlord or to any then  existing  or  prospective  lender,
investor or  purchaser,  with respect to the Master  Lease  Property or any
part thereof,  designated by Landlord,  a written statement  certifying (i)
that  this  Lease is in full  force  and  effect  (if such is the case) and
unmodified (or, if modified, stating the nature of such modification), (ii)
the date to which Rent has been paid, (iii) that there are not, to Tenant's
actual knowledge, any uncured defaults by Landlord or Tenant (or specifying
such defaults if any are claimed),  and (iv) such other matters as Landlord
may reasonably  request.  Any such statement may be relied upon by any such
then existing or prospective lender, investor or purchaser. If Tenant fails
to deliver such  statement  within the ten (10)  business day period and if
following the  expiration of that period  Landlord  gives a second  written
request for the statement and Tenant fails to deliver the statement  within
five (5) business days after the second request,  Tenant shall conclusively
be deemed to have responded that this Lease is in full force and effect and
unmodified and that there are no uncured defaults in Landlord's performance
hereunder.

                  (e) Brokers.  Each party  represents  and warrants to the
other that no broker  procured this Lease on its behalf and that such party
had no conversations or negotiations with any broker concerning the leasing
of the Master Lease Property, other than Barnes, Morris, Pardoe and Foster,
which firm is receiving a  commission  from Tenant in  connection  with the
Purchase  and  Sale  Agreement  and  is not  entitled  to a  commission  in
connection  with this Lease.  Each party shall  indemnify the other against
liability in connection with a breach of its representation and

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warranty  in  this  Subsection  and in  connection  with  any  claim  for a
brokerage  or finder's  commission  or fee  arising  out of its acts.  This
indemnification shall survive any termination of this Lease.

                  (f) Applicable Law. This Lease and all matters  pertinent
thereto shall be construed and enforced in accordance  with the  Applicable
Laws of the State of Maryland, excluding choice of laws principles.

                  (g) Entire Agreement.  This Lease, including all exhibits
hereto,  constitutes the entire  agreement  between the parties hereto with
respect to the leasing of the Master Lease Property and may not be modified
except by an instrument in writing executed by the parties hereto.

                  (h) Binding Effect.  This Lease and the respective rights
and  obligations of the parties hereto shall inure to the benefit of and be
binding upon the  successors  and assigns of the parties  hereto as well as
the parties themselves; subject, however, to Subsection (o) below.

                  (i) Survival. All provisions of this Lease which by their
express terms survive  termination  of this Lease or which by the operation
of their terms are  intended to be  performed,  in whole or in part,  after
termination of this Lease, shall survive any termination of this Lease.

                  (j) Severability. If any provision of this Lease shall be
held to be invalid,  void or unenforceable,  such provision shall be deemed
reformed  to be valid,  in effect  and  enforceable,  and to be as close in
meaning  and  intent as the  defective  provision  and still the  remaining
provisions  hereof  shall not be affected or impaired,  and such  remaining
provisions shall remain in full force and effect.

                  (k)  Headings,  Gender,  etc. As used in this Lease,  the
word "person"  shall mean and include,  where  appropriate,  an individual,
corporation,  partnership or other entity;  the plural shall be substituted
for the singular,  and the singular for the plural, where appropriate;  and
words of any gender shall include any other gender. The topical headings of
the  several  paragraphs  of this  Lease are  inserted  only as a matter of
convenience and reference, and do not affect, define, limit or describe the
scope or intent of this Lease.  References  in this Lease to  Sections  and
Subsections are references to Sections and Subsections of this Lease.

                  (l) Waiver of Jury. To the extent permitted by Applicable
Laws,  each of Landlord and Tenant hereby waives any right it may have to a
jury  trial  in  the  event  of  litigation  between  Landlord  and  Tenant
pertaining to this Lease.

                  (m)      Landlord's Right to Cure.  Landlord may, but shall
not be obligated to, cure any default by Tenant, specifically including,  but

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not  by  way  of  limitation,   Tenant's  failure  to  pay Impositions,  obtain
Insurance,  Care for the Master  Lease  Property,  or satisfy lien claims,
after complying with any applicable  notice and cure provisions  established
under this Lease; and whenever Landlord so elects, all  reasonable out of
pocket costs and expenses paid by Landlord in curing such default,  including,
without limitation,  reasonable attorneys' fees, shall be Additional Rent due
on the next scheduled Rent payment date.

                  (n)  Relationship of Parties.  Nothing  contained  herein
shall be deemed or construed by the parties hereto, nor by any third party,
as creating the  relationship of principal and agent or of partnership,  or
of joint venture by the parties hereto, it being understood and agreed that
no  provision  contained  in this Lease nor any act of the  parties  hereto
shall be deemed to create any  relationship  other than the relationship of
Landlord and Tenant.

                  (o) Landlord Means Owner.  The term "Landlord" as used in
this lease,  so far as covenants or obligations on the part of Landlord are
concerned, shall be limited to mean and include only the owner or owners at
the time in question of the Master Lease  Property and, in the event of any
transfer or  transfers  of the title to all of the Master  Lease  Property,
Landlord  herein  named  (and  in  case  of  any  subsequent   transfer  or
conveyances,  the then grantor) shall be automatically  freed and relieved,
from and after the date of such transfer or conveyance, of all liability as
respects the  performance  of any covenants or  obligations  on the part of
Landlord  contained in this Lease  thereafter to be performed  (but not any
liabilities accrued prior to the date of transfer); provided that any funds
in the  hands  of such  Landlord  or the then  grantor  at the time of such
transfer,  in which  Tenant has an  interest,  shall be turned  over to the
grantee,  and any amount  then due and payable to Tenant by Landlord or the
then grantor under any  provisions  of this Lease,  shall be paid to Tenant
and  further  provided  that the  transferee  assumes in writing all of the
covenants  and  obligations  of Landlord to observed  and  performed on and
after the date of transfer.

                  (p) References to Size.  Landlord and Tenant  acknowledge
and agree that any  references  in this Lease to the size of the  Property,
the Main Building  Area,  the Main Building or any portion  thereof are for
convenience only and regardless of whether the actual size of such areas is
greater or less than the size stated in this Lease,  all obligations of the
parties hereunder, including without limitation, the obligation to pay Rent
shall remain the same and shall not be affected by any errors in references
to size.

                  (q) Unavoidable  Delays.  For purposes of this Lease, the
term  "Unavoidable  Delays" shall mean delays caused by strikes,  lockouts,
acts  of  God,  inability  to  obtain  labor  or  materials,   governmental
restrictions or inaction,  enemy action,  civil commotion,  fire, terrorist
action, epidemic, public utility failure,  unavoidable  casualty,  moratorium

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or similar  laws  prohibiting performance,  weather conditions or any other
similar matter which shall be beyond the  reasonable  control of Landlord or
Tenant, as the case way be; but the lack or  insufficiency of funds shall not 
constitute an Unavoidable Delay.

                  (r) Landlord's Approvals.  Wherever Landlord's consent or
approval  are  required  under  this  Lease,   Landlord  shall  approve  or
disapprove  the matter within ten (10) business days after Tenant  requests
the  consent or approval  in  writing.  If Landlord  fails to do so and if,
following the expiration of the ten (10) business day period,  Tenant gives
a second written  request for the consent or approval and Landlord fails to
approve or  disapprove  the matter  within five (5) business days after the
second request,  Landlord shall conclusively be deemed to have consented to
or approved the matter, as the case may be.

                  (s) Rate of  Interest.  If any amount owed by Landlord to
Tenant under this Lease remains  unpaid after such amount is due and notice
thereof  has been given to  Landlord,  the  outstanding  amount  shall bear
interest at the  Stipulated  Rate from the date such amount is due and such
notice is given to the date such amount is paid.

                  (t)  Cooperation  of  Parties.  Whenever  the parties are
required to cooperate  with each other under this Lease but are entitled to
reimbursement  for their  out-of-pocket  costs to third parties,  the party
that is  obligated  to  cooperate  shall  provide an estimate of such third
party costs to the party  requesting such  cooperation and obtain the prior
written  approval from such other party not to be unreasonably  withheld or
delayed before such costs are incurred.

                  (u)  Reconciliation.  Nothing in this Lease shall prevent
or impair Tenant from performing its obligations or observing its covenants
under the  Existing  Space  Leases.  Further,  nothing in this Lease  shall
prevent or impair any of the Existing  Tenants from exercising their rights
and privileges under the Existing Space Leases. No such action by Tenant or
the Existing  Tenants in accordance with the Existing Space Leases shall be
deemed to be a breach or default by Tenant under this Lease.

                  (v) Memorandum of Lease. Upon request of either party the
other party shall promptly  execute and deliver a memorandum or other short
form  version of this  Lease  setting  forth the basic  terms of this Lease
excluding Rent. The party recording such memorandum, short form version, or
other  document  giving  notice  of  this  Lease  shall  pay  any  and  all
recordation and transfer taxes due in connection with such recordation.

                  (w)  Financial  Reports.  In the event that  Tenant is no
longer a publicly  traded  company with common stock  trading on either the
New York Stock  Exchange,  the American  Stock Exchange or the NASDAQ Stock
Exchange (or, in the event the Tenant's stock is no longer traded on such 

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exchanges, or a successor or reasonably equivalent exchange), Tenant shall
supply Landlord,  within ten (10) business days of Landlord's  request
therefor (to be no more  frequent than once per year), copies of Tenant's most
recent  financial  reports.  Such reports shall (i) include an income
statement,  balance sheet,  statement owner's equity and statement  of cash
flows,  (ii)  shall be audited  by a  certified  public accountant  or, to the
extent audited  Financial  Reports are not otherwise obtained by Tenant for
other  purposes,  certified  by the chief  financial officer of  Tenant,  to
his/her  knowledge,  as being  true,  correct  and complete financial  reports,
and (iii) shall be dated no later than twelve months prior to Landlord's
request.  Notwithstanding the foregoing,  in the event that Landlord  requests
such  financial  reports  within one hundred twenty (120) days after Tenant's
fiscal year end,  Tenant shall have up to one  hundred  twenty  (120) days
from such  fiscal  year end to supply such reports to  Landlord;  provided
Tenant has given  Landlord its most recent financial reports and such reports
are not dated earlier than twelve (12) months prior to Tenant's fiscal year end.

                  (x)  Landlord's  Affiliates.   Notwithstanding   anything
contained  in  this  Lease  to the  contrary,  any  act or  omission  of an
affiliate  of  Landlord  on any  Excluded  Areas  shall not be a default of
Landlord under this Lease. In no event shall this provision be construed in
any  manner as a waiver of any right  that  Tenant  has at law or in equity
against such affiliate as a result of such act or occurrence.


                          [SIGNATURE PAGE FOLLOWS]

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                  IN WITNESS  WHEREOF,  the parties hereto have caused this
Lease to be executed as of the day and year stated herein.

                                 LANDLORD:

                                 LCOR CLARKSBURG L.L.C.
                                 By: Clarksburg Management, Inc.

                                 By:/s/ Michael T. Goulder

                                 Name: Michael T. Goulder

                                 Title: Vice President



                                 TENANT:

                                 COMSAT CORPORATION


                                 By: /s/ Allen E. Flower

                                 Name: Allen E. Flower

                                 Title: Vice President and
                                        Chief Financial Officer



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                                 SCHEDULE I
                               Defined Terms

         AAA:                             Section 11(c)
         ACM:                             Section 27(b)
         Accelerated Payment:             Section 21(b)(iii)(A)
         Additional Easements:            Section 6(f)
         Additional Rent:                 Section 4(b)
         Adequate Assurance of
           Future Performance:            Section 22(d)
         All Risks Policy:                Section 14(a)(i)
         Alterations:                     Section 13(a)
         Applicable Laws:                 Section 5(b)(iv)
         Appurtenances:                   Section 6(d)
         Arbitration Deadline:            Section 28(d)
         Architect:                       Section 15(b)(i)
         Assignment:                      Section 19(b)
         Base Rent:                       Section 4(a)
         Blanket Policy:                  Section 14(e)
         Building A, B or C:              Definitions of Main Building
         Care, Care for,
           Care of:                       Section 11(a)
         Communication Facilities:        Section 6(a)(iii)
         Comparable Buildings:            Section 11(a)
                  Comparable Properties:  Section 11(b)
         Contents:                        Section 27(e)
         Damage:                          Section 15(a)
         Declaration:                     Section 11(b)
         Default Measuring Period:        Section 21(b)(iii)(B)
         Development:                     Section 6(a)
         Effective Date:                  Preamble
         Environmental Conditions:        Section 27(a)
         Escrow Account:                  Section 21(b)(iii)(B)
         Escrowee:                        Section 21(b)(iii)(B)
         Events of Default:               Section 21(a)
         Existing Space Leases:           Section 19(a)
         Existing Tenants:                Section 19(a)
         Facilities Lease:                Section 21(a)(iii)
         Flood and Earthquake
           Insurance:                     Section 14(f)
         Flood Zone:                      Section 14(f)
         Hazardous Material:              Section 27 and 27(d)
         Holdover Notice:                 Section 3(b)(i)
         Holdover Period:                 Section 3(b)(i)
         Holdover Space:                  Section 3(b)(ii)
         Impositions:                     Section 7(a) and (d)
         Indemnifying Party:              Section 16(c)
         Indemnitee:                      Section 16(c)
         Indemnity Payment:               Section 16(c)
         Initial Term:                    Section 3(a)
         Institutional Mortgagee:         Section 15(c)(i)
         Insurable Casualty:              Section 15(h)
         Insurance:                       Section 14(a)
         Insurance Notice:                Section 14(g)

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                            SCHEDULE I (cont'd)

         Insurance Trustee:               Section 15(c)
         Landlord:                        Preamble; Section 30(o)
         Landlord Approved SNDA:          Section 19(b)
         Lease:                           Preamble
         Lease Renewal:                   Section 19(d)
         Lease Year:                      Section 3(c)
         Liability Policy:                Section 14(a)(ii)
         Measuring Period:                Section 19(d)
         Mitigation Leases:               Section 21(b)(iii)(B)
         Mortgagee:                       Section 7(e)(i)
         Non-Broker Sublease:             Section 19(b)
         Non-Consensual Holdover
           Period:                        Section 24
         Operating Expenses:              Section 21(b)(iii)(B)
         Personal Property:               Section 13(b)
         Plans:                           Section 13(a)(i)
         Post Default Leases:             Section 21(b)(iii)(B)
         Preapproved Alterations:         Section 13(a)
         Prime Rate:                      Section 4(h)
         Profit:                          Section 19(d)
         Purchase and Sale
           Agreement:                     Recital (a)
         Remediation Obligation:          Section 27(a)
         Renewal Notice:                  Section 28(b)
         Renewal Option,
           Renewal Term:                  Section 28(a)
         Rent:                            Section 4(b)
         Rent Insurance:                  Section 14(a)(iv)
         Replacement Value:               Section 14(a)(i)
         Requisition:                     Section 15(c)(i)
         Restoration:                     Section 15(a)
         Restricted Areas:                Section 12(a)
         Restricted Property:             Section 13(b)
         Roof Based Facilities:           Section 13(a)
         Roof Work:                       Section 11(e)
         Security Deposit:                Section 29
         Seismic Activity Zone:           Section 14(f)
         Signs:                           Section 9(a)
         Standard Rating:                 Section 14(g)
         Stipulated Rate:                 Section 4(h)
         Sublease:                        Section 19(b)
         Sublease Arbitration
           Deadline:                      Section 19(c)
         Subject Space:                   Section 19(d)
         Subtenant:                       Section 19(e)
         Taken, Taking:                   Section 17(a)(i)
         Tax and Insurance
           Holdbacks:                     Section 21(b)(iii)(B)
         Tenant:                          Preamble
         Tenant Approved SNDA:            Section 20(a)
         Tenant's Knowledge:              Section 15(c)(ii)
         Term:                            Section 3(a)
         Third Party Claim:               Section 16(d)(i)

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         Triggering Event:                  Section 6(b)
         Unavoidable Delays:                Section 30(q)
         Utilities:                         Section 8(a)

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                                Schedule II
                                Deductibles


I.       All Risk Policy                             $100,000
         Flood and Earthquake Insurance              $150,000


II.      In the event that Tenant's corporate debt drops below BB, as rated
         by an Approved  Credit Rating  Agency,  the following  deductibles
         shall apply:

         All Risk Policy                             $25,000
         Flood and Earthquake Insurance              $50,000


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                            SCHEDULE OF EXHIBITS



   EXHIBIT                                             SECTION

   Exhibit A         (Description of Land)             1(a)

                  Exhibit B (Description of Main       1(a)
                             Building Area)

                  Exhibit C (Description of            1(a)
                             Installations Premises)

                  Exhibit D  Intentionally Omitted

                  Exhibit E  (Wire Instructions)       4(g)

                  Exhibit F  (Roof Work)               11(e)

                  Exhibit G  (Existing Space Leases)   19(a)

                  Exhibit H  (Landlord Approved SNDA)  19(b)

                  Exhibit I  (Tenant Approved SNDA)    20(a)

                  Exhibit J  (Operations and           27(b)
                              Maintenance Plan)


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